Part II - Elements of Prohibited Force

Introduction

Having unentangled the relationship between the UN Charter and the customary prohibition of the use of force in Part I and thus determined that the most suitable approach to identifying the meaning of prohibited force is to focus on treaty interpretation, Part II will carry out a textual analysis of article 2(4) of the UN Charter to identify the elements of prohibited force.

Some argue that due to the special nature of the UN Charter, different rules should apply to its interpretation than to other treaties.¹ However, whatever its unique character within the international legal system, the UN Charter is a multilateral treaty, ‘and as such subject to the general law of treaties’.² Article 5 of the Vienna Convention on the Law of Treaties³ (VCLT) confirms that ‘[t]he present Convention applies to any treaty which is the constituent instrument of an international organization … without prejudice to any relevant rules of the organization’.⁴ The approach set out in article 5 of the VCLT was confirmed by the International Court of Justice (ICJ) in the Nuclear Weapons Advisory Opinion, in which it held that: ‘From a formal standpoint, the constituent instruments of international organizations are multilateral treaties, to which the well-established rules of treaty interpretation apply.’⁵ The ICJ has held more specifically with respect to the UN Charter that ‘[o]n the previous occasions when the Court has had to interpret the Charter of the United Nations, it has followed the principles and rules applicable in general to the interpretation of treaties, since it has recognized that the Charter is a multilateral treaty, albeit a treaty having certain special characteristics’.⁶

The starting point for interpreting article 2(4) of the UN Charter is therefore to apply the process set out in the VCLT. The general rule of interpretation and the rule on supplementary means of interpretation are set out in articles 31 and 32 of the VCLT, which both apply as rules of customary international law.⁷ Article 31(1) of the VCLT sets out the general rule of interpretation as follows: ‘A treaty shall be interpreted in good faith in accordance with the ordinary meaning to be given to the terms of the treaty in their context and in the light of its object and purpose.’ According to article 31(3) of the VCLT:

There shall be taken into account, together with the context:

1. (a) any subsequent agreement between the parties regarding the interpretation of the treaty or the application of its provisions;

2. (b) any subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation;

3. (c) any relevant rules of international law applicable in the relations between the parties.

This work will thus apply the following principles to the interpretation of a prohibited ‘use of force’ under article 2(4) of the UN Charter:

• focus on a textual interpretation of article 2(4) by looking at the ‘ordinary meaning to be given to the terms of the treaty in their context and in the light of its object and purpose’;⁸

• take into account ‘subsequent agreements between the parties regarding the interpretation of the treaty or the application of its provisions’ and ‘subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation’, together with ‘any relevant rules of international law applicable in the relations between the parties’;⁹

• where appropriate, consider preparatory work of the UN Charter and ‘other subsequent practice’ as a supplementary means of interpretation;¹⁰ and

• examine how the term ‘use of force’ is currently interpreted and applied by States.

Part II will apply these principles to a textual analysis of article 2(4), including subsequent agreements of States, to identify the elements of prohibited force.

4 Contextual Elements of a Prohibited ‘Use of Force’ International Relations

Introduction

The text of article 2(4) reads as follows:

The Organization and its Members, in pursuit of the Purposes stated in Article 1, shall act in accordance with the following Principles.

(4) All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.

This chapter will carry out a textual analysis of the terms of article 2(4) of the UN Charter other than ‘threat or use of force’,¹ in order to delineate the contextual elements of prohibited force. These terms – ‘all Members’, ‘international relations’ and ‘against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations’ – are fundamental, contextual elements that must be present in order for a ‘use of force’ to fall within the scope of article 2(4). This chapter will briefly examine each of these terms in turn to understand how they delineate the scope and context of a prohibited ‘use of force’.

‘All Members’

States Only

In the first place, the prohibition in article 2(4) binds only States, as confirmed by State practice and case law.² With respect to the parallel customary rule, it is an interesting question whether the customary prohibition also applies only to States or if it also binds non-State actors, international organisations or individuals.³

Member States Only

As a treaty, the provisions of the UN Charter are clearly binding on its parties, that is, the Member States of the United Nations. Non-Member States are bound by the prohibition only indirectly through the UN Charter (since they could be subject to enforcement action/sanctions for failing to comply with the relevant principles),⁴ but the source of their legal obligation is customary international law.

Use of Force by Non-State Armed Groups

In certain circumstances, State support or involvement in forcible acts of other States, or in forcible acts of non-State actors against another State will violate the prohibition of the use of force.⁵ However, this is relevant not to who are the addressees of the prohibition (States) but to what acts or level of support will result in attribution to a State or amount to an indirect ‘use of force’ in violation of article 2(4). With respect to attribution, the general principles of State responsibility apply, as set out in articles 4 to 11 of the International Law Commission (ILC) Articles on State Responsibility. In particular, article 8 of the ILC Articles on State Responsibility provides that:

The conduct of a person or group of persons shall be considered an act of a State under international law if the person or group of persons is in fact acting on the instructions of, or under the direction or control of, that State in carrying out the conduct.

The International Court of Justice (ICJ) had applied a similar standard of attribution in the Nicaragua case, in which it held that:

For this conduct to give rise to legal responsibility of the United States, it would in principle have to be proved that that State had effective control of the military or paramilitary operations in the course of which the alleged violations were committed.⁶

Although the International Criminal Tribunal for the former Yugoslavia in the Tadic case applied a different test for attribution of ‘overall control’,⁷ this has been criticised by both the ILC⁸ and the ICJ, which declined to adopt this standard.⁹ Other forms of support that do not meet the standard for attribution of the conduct of the non-State armed group to a State may nevertheless constitute an indirect ‘use of force’ by a State under article 2(4) of the UN Charter. Indirect force is discussed further in Chapter 5.

‘Shall refrain … from’

This is obligatory language that reflects the binding legal obligation set out in article 2(4).

‘in their international relations’

The confinement of the prohibition of the threat or use of force by States to those ‘in their international relations’ ‘continues the tradition of article I of the Kellogg-Briand Pact, which confines the scope of application of the prohibition of the recourse to war as an instrument of national policy to the realm of the “solution of international controversies”’.¹⁰ This section will discuss the meaning of the term ‘international relations’ and whether it requires that the object of a prohibited use of force be another State, as well as looking at the types of acts that fall within and outside the scope of this term.

Another State?

The wording of article 2(4), in particular the terms ‘international relations’ and ‘in any other manner’, does not explicitly require the damage to be to another State.¹¹ The reference to ‘international relations’ implies that a prohibited use of force must affect the relations between the State using force and another State. This leaves open the possibility that the actual damage is not to a State but affects inter-State relations. With respect to the phrase, ‘in any other manner’, the second half of article 2(4) was introduced to prevent loopholes in interpretation (see discussion of this term later in the chapter). Thus, interpreting the term ‘international relations’ to prohibit another type of use of force (in addition to uses of force against the territorial integrity or political independence of a State) would comply with this intended purpose of making the prohibition more expansive. Furthermore, a natural reading of the second part of article 2(4) is to read the listed elements conjunctively (i.e. as alternatives). This would result in the following categories of prohibited conduct: firstly, uses of force in the international relations of Members against the territorial integrity or political independence of any State, and secondly, uses of force in the international relations of Members in any other manner inconsistent with the Purposes of the United Nations.¹²

This interpretation would potentially encompass a use of force that is in ‘international relations’ outside the context of State damage, such as damage to terra nullius. Claus Kreß notes that ‘[i]t is an unsettled question whether the use of force by a state … on terra nullius occurs in international relations and thus within the meaning of article 2(4) of the UN Charter’.¹³ Since there are hardly any areas of terra nullius (rare examples include Bir Tawil between Egypt and Sudan, an area that neither claims, and parts of Antarctica), this issue is unlikely to be raised in practice. However, both on Earth (with respect to the high seas)¹⁴ and in outer space (with respect to celestial bodies),¹⁵ there are vast areas which do not form part of the territory of any State and are not subject to claims of sovereignty, so it is conceivable that a ‘use of force’ could be directed against these environments (for instance, as part of a malicious attack, or in the process of exploiting natural resources located in these environments), thus raising the question of whether such an act occurs in ‘international relations’ even though no State suffers direct damage.

Object and Purpose

The object and purpose of the UN Charter and in particular article 2(4) are also relevant to determining whether the range of interpretive possibilities of the term ‘international relations’ includes damage to objects without a nexus to another State.¹⁶ Subsequent agreements with respect to article 2(4) of the UN Charter demonstrate the agreement of Member States that the primary purposes of that provision are international peace and security and the sovereign equality of States.¹⁷ The Friendly Relations Declaration emphasises international peace and security as among the fundamental purposes of the UN Charter¹⁸ and sets out related principles that are ‘interrelated with’¹⁹ the prohibition of the use of force, including the obligation to settle international disputes by peaceful means²⁰ and the principle of sovereign equality of States.²¹ Resolution 42/22 (1987) also notes that the principle of peaceful settlement of disputes ‘is inseparable from the principle of refraining from the threat or use of force in their international relations’.²² Resolution 42/22 explicitly reaffirms the purpose of article 2(4) is the ‘establishment of lasting peace and security for all States’.²³ In the 2005 World Summit Outcome Document (adopted by consensus), the UN General Assembly emphasised the purposes of the UN Charter as international peace and security and sovereign equality of States. In that document, the UN General Assembly ‘reaffirm[ed] that the purposes and principles guiding the United Nations are, inter alia, to maintain international peace and security, to develop friendly relations among nations based on respect for the principles of equal rights and self-determination of peoples and to take other appropriate measures to strengthen universal peace’.²⁴ These two primary values protected by article 2(4) – international peace and security and the sovereign equality of States – give rise to arguments for and against including uses of force that are not against a State, depending on which purpose is emphasised, as discussed below.

State Sovereignty

Article 2(4) of the UN Charter protects sovereign equality by prohibiting the use of force to settle international disputes. The term ‘of any state’ suggests that the protected object of article 2(4) is States, and in particular their ‘territorial integrity’ and ‘political independence’. This is also supported by the Friendly Relations Declaration, which holds that the principle of sovereign equality of States includes the inviolability of the territorial integrity and political independence of the State.²⁵ (The protected interest of State sovereignty in article 2(4) read together with articles 2(3) and 2(7) also supports an interpretation of a ‘use of force’ as requiring a coercive intent – this is discussed further in Chapter 6.) The protected object of State sovereignty tends to exclude the use of force against objects with no sufficient nexus to another State from the scope of article 2(4).

International Peace and Security

However, the second and arguably main purpose of article 2(4), the maintenance of international peace and security, may concern damage to non-State objects (objects with no sufficient nexus to another State) under certain circumstances. This possibility is supported firstly by the Purposes of the United Nations, and secondly by reading article 2(4) in the context of the collective security framework provided for in the Charter.²⁶ The Purposes are referred to in the chapeau of article 2, which provides: ‘The Organization and its Members, in pursuit of the Purposes stated in Article 1, shall act in accordance with the following Principles’ (one of which is of course the principle of the prohibition of the use of force in article 2(4)). The first of the Purposes set out in article 1 in paragraph 1 is

To maintain international peace and security, and to that end: to take effective collective measures for the prevention and removal of threats to the peace, and for the suppression of acts of aggression or other breaches of the peace, and to bring about by peaceful means, and in conformity with the principles of justice and international law, adjustment or settlement of international disputes or situations which might lead to a breach of the peace.

The Preamble of the UN Charter (which according to article 31(2) of the VCLT comprises part of the context for the purpose of treaty interpretation) further supports this as the primary value of article 2(4). The Preamble states in its opening lines, ‘[w]e the peoples of the United Nations determined to save succeeding generations from the scourge of war’. In the first meeting of Commission 1 (responsible for drafting the general provisions of the UN Charter including the preamble, Purposes and Principles) at the San Francisco Conference, the President of the Commission, Mr Rolin of Belgium, stated with respect to the ‘first object’ of the maintenance of peace: ‘We are not state worshippers, and when we speak of the prevention of war we have, of course, in mind only what sufferings war is causing to humanity’.²⁷ In its Advisory Opinion on Certain Expenses, the ICJ held that ‘[t]he primary place ascribed to international peace and security is natural, since the fulfilment of the other purposes will be dependent upon the attainment of that basic condition’.²⁸

The primary purpose of article 2(4) as the maintenance of international peace and security is also supported by the context of the collective security framework provided for in the Charter.²⁹ The UN Charter sets out two exceptions to the prohibition of the use of force, namely, self-defence in response to an armed attack under article 51 and the authorisation of force by the UN Security Council acting under Chapter VII. These provisions (article 2(4), article 51 and Chapter VII) together comprise the collective security system of the United Nations; under international law in the post-Charter era, States do not have a right to unilaterally use force but must settle their international disputes by peaceful means. This system is supplemented by the customary international law duty of non-intervention (in recognition of the sovereign equality of States). The context of article 2(4) and its relationship with other Charter provisions illuminates the interpretation of article 2(4) by emphasising its primary aim of maintaining international peace and security. In this light, the purpose of maintaining international peace and security points towards the inclusion of forcible acts against non-State objects within the scope of the prohibition, when those acts affect the international relations between States and therefore endanger international peace and security.

In sum, the text of article 2(4) does not unambiguously require that a State be the object or target of a ‘use of force’, and the primary value protected by article 2(4) of international peace and security supports a broad interpretation. During the drafting of the 1970 Friendly Relations Declaration, ‘[t]hose who discussed the point generally agreed that the term had the effect of limiting the prohibition in Article 2, paragraph 4, to disputes between States’.³⁰ However, this does not constitute a ‘subsequent agreement’ within the meaning of article 31(3) of the VCLT, and such an interpretation remains to be either confirmed or rejected through the subsequent agreement and subsequent practice of States. So far this author is not aware of any State practice seeking to extend the interpretation of article 2(4) beyond damage to States. While a broader interpretation remains textually open, since article 2(4) also protects States’ sovereignty and territorial integrity, it is likely that another State must be the object/target in order for a ‘use of force’ to be in ‘international relations’ and fall within the scope of article 2(4).

Required Nexus

This then raises the question of the required nexus between the object/target of a use of force and another State, particularly with respect to forcible acts against non-State objects such as nationals of a State, individuals present within the territory of a State or private property such as private and merchant vessels or aircraft registered to a State. In some cases, attacks on individuals due to their nationality have been regarded as armed attacks (and therefore uses of force under article 2(4)) against the State of nationality, such as the Entebbe incident, where all hostages were released apart from those of Israeli nationality.³¹ In certain circumstances, article 2(4) applies to uses of force by a State against private vessels and aircraft registered to another State. This results from article 3(g) of the Annex to 1974 General Assembly Resolution 3314, which lists as an act of aggression an ‘attack by the armed forces of a State on the … marine and air fleets of another State’. The issue of required nexus to another State is of particular relevance to emerging forms of practice in disputed maritime zones such as in the South China Sea, firstly, with respect to ‘[t]he use of Coast Guard and other maritime law enforcement agency vessels and officials, and indeed merchant vessels and fishing vessels under obvious governmental orders, to enforce presence and to employ force in disputed maritime areas’ and, secondly, to ‘the use of private citizens – especially fishermen – to assert claims, act as state proxies in confrontation situations, or to provoke harassment which is then used to justify escalated intervention by more formal state forces such as Coast Guard vessels’.³² For non-State objects/targets that do not have a close association with a State, more will be required to bring the act within ‘international relations’ and into the scope of article 2(4), such as the presence of other factors including the gravity of the (potential) effects, a coercive or hostile intent against a State or a pre-existing dispute between States.

Political Context

If there is a pre-existing dispute between the States concerned, such as contested territory, this may bring the use of force within the realm of ‘international relations’ and thus within the scope of the jus contra bellum.³³ The political context may be relevant to whether the act itself constitutes a ‘use of force’, since it may increase the gravity of the act and indicate a hostile or coercive intention. A pre-existing dispute between States or otherwise hostile relations could thus explain why friendly States do not view certain acts as an unlawful ‘use of force’, which, if committed by an unfriendly State, would be so regarded. The State experiencing the forcible act (the ‘victim’ State) will interpret the intention or motivation of the forcible act and the perceived threat to its security (gravity) taking into account this political context; thus, the interpretation of the situation is influenced by this context, meaning that the State could in fact be applying the same criteria for a ‘use of force’ but to differently viewed ‘facts’. For example, when on 1 March 2007, 170 Swiss Army infantry troops armed with rifles lost their bearings and crossed the border into Liechtenstein, the incursion did not provoke any official protest.³⁴ It is easy to imagine that the response and legal characterisation of such an incursion would be vastly different if it occurred between States with heightened tensions or pre-existing disputes, such as India/Pakistan or Democratic People’s Republic of Korea/South Korea. The relationship between intention, gravity and international relations is explored further in Chapter 8. A ‘use of force’ in the context of an existing international dispute may also relate to whether the act is ‘in any other manner inconsistent with the Purposes of the United Nations’ (the second part of article 2(4), discussed later), since such a use of force is inconsistent with the Purpose to maintain international peace and security through the peaceful settlement of international disputes (article 1(1), UN Charter).

The remainder of this section will look at particular categories of acts falling within and outside the scope of the term ‘international relations’.

Extra-Territorial Sovereign Manifestations of a State

The classic paradigm is a use of force by a State on the territory of another State,³⁵ but ‘international relations’ also covers a use of force against an extraterritorial sovereign manifestation of a State including on the high seas or on the territory of the State using force, such as armed forces or embassies.³⁶

Disputed Territory and Armistice Lines

In the case of disputed territory that is claimed by more than one State, the prohibition of the use of force acts in favour of the State in de facto control of the territory even against the State holding the sovereign title.³⁷ This is an example of a use of force against another State that does not violate its territorial integrity. Kreß suggests that what is being protected by the prohibition in such a case is ‘the peaceful common life on the disputed territory and the maintenance of international peace and security’.³⁸ However, this interpretation is without prejudice to the right of a victim State to act in self-defence against a State that has established military occupation over its territory as a result of an armed attack under article 51;³⁹ a State may not use force against a State in de facto control of its territory unless it is in self-defence or with UN Security Council authorisation.⁴⁰ A ‘use of force’ is also in ‘international relations’ and falls within the scope of article 2(4) if it ‘“violate[s] international lines of demarcation, such as armistice lines, established by or pursuant to an international agreement to which it is a party or which it is otherwise bound to respect”, provided that these lines run between two states’. Kreß argues that in the case of disputed territory and armistice lines, ‘international law subordinates the protection of territorial sovereignty to the protection of a peaceful common life on a certain piece of territory and the maintenance of international peace and security’.⁴¹ With respect to entities whose statehood is disputed (e.g. North and South Vietnam during the Vietnam War; North and South Korea during the Korean War; Taiwan; Kosovo; Abkhazia; South Ossetia), the situation is more complicated. The jus contra bellum does not require all States to recognise the statehood of the entity in question, and it is an open question if article 2(4) covers a use of force violating an ‘international demarcation line delimiting the territory of a non-State political entity’.⁴²

Use of Force by a State within Its Own Territory

An interesting question is raised as to whether and when a use of force by a State within its own territory is in ‘international relations’ and falls within the scope of article 2(4). Differing views were expressed on the inclusion of the use of force within a State within the scope of the prohibition during the drafting of the 1970 Friendly Relations Declaration. In the 1966 meeting of the Special Committee on Principles of International Law concerning Friendly Relations and Co-operation among States (‘Special Committee’), one representative suggested the Special Committee include a statement that ‘the prohibition on the threat or use of force did not in any way affect the use of force within a State’.⁴³ In the 1970 meeting of the Special Committee,

[t]he Italian delegation reiterated, with respect to the prohibition of the threat or use of force, its firm opinion that that prohibition was, according to the Charter, a general prohibition which must be complied with under any circumstances other than the exceptions contemplated in the Charter … including, inter alia, the high seas, outer space and, as his delegation had stressed at the Committee’s eighty-ninth meeting in 1968 … even the very territory of the States to which the prohibition was addressed.⁴⁴

However, this point was not further discussed and does not appear in the text of the Friendly Relations Declaration.

The use of force within a State’s own territory can be further broken down into several types of incidents, namely, a use of force by a State in its own territory: (a) against its own population, (b) against territorial incursion by the armed forces of another State, and (c) against foreign private actors such as individuals, merchant vessels or civilian aircraft. These are briefly dealt with in turn in the following sections.

A. Use of Force within a State’s Own Territory against Its Own Population

The Nuclear Weapons Advisory Opinion can be interpreted as excluding uses of force by a State ‘within its own boundaries’ from the scope of the prohibition in article 2(4) since the Court decided not to deal with this issue.⁴⁵ However, the contrary interpretation is also possible, since the ICJ stated that ‘[t]he terms of the question put to the Court by the General Assembly in resolution 49175 K (“Is the threat or use of nuclear weapons in any circumstance permitted under international law?”) could in principle also cover a threat or use of nuclear weapons by a State within its own boundaries’, and decided that it was not called upon to deal with an internal use of nuclear weapons because no State addressing the Court raised this issue.⁴⁶ Kreß notes that ‘it would probably overstate the significance’ of the Court’s statement to conclude that the Court would totally exclude all uses of force by a State within its territory from the prohibition,⁴⁷ but he does note that it is uncontroversial that a use of force by a State against its own population within its territory would not fall within the scope of the prohibition,⁴⁸ although this may well violate other norms of international law including international human rights and humanitarian law.

B. Legal Basis for Forceful Response by a State to Small-Scale Territorial Incursions by Armed Forces of Another State

It is controversial whether a use of force by a State within its own territory against small-scale intruding police or military units of another State (including ships and aircraft) falls within the scope of the prohibition of the use of force in article 2(4). The crux of the debate is the legal basis for a forcible response by a State to low-scale incursions within its own territory, with some arguing that the legal basis is law enforcement based on the exercise of sovereign jurisdiction,⁴⁹ and others arguing that the legal basis is the jus contra bellum as it engages international relations (and that it is therefore restricted with respect to territorial incursion falling short of armed attack).⁵⁰

Ian Brownlie argued that forcible response to aerial trespass (but not maritime trespass)⁵¹ is a justified exception to the prohibition of the use of force, separate from self-defence. He sets out some specific requirements that must be met for the exception to apply:

In general the practice seems to be that there is no right to shoot down trespassers unless they refuse or appear to refuse to land. However, if the penetration is by unidentified fast aircraft which persist in a deliberate and deep penetration of airspace, it may be that, in view of the destructive power of even a single nuclear weapon carried by an aircraft, the territorial sovereign is justified in taking without any warning violent and immediate preventive measures.⁵²

He argued that ‘[t]his is a rare instance in which a use of force may be justified although no actual attack has occurred’.⁵³

Judge Stephen Schwebel in his dissenting opinion in the Nicaragua case argued that ‘contemporary international law recognizes that a third State is entitled to exert measures of force against the aggressor on its own territory and against its own armed forces and military resources’.⁵⁴ Judge Schwebel quotes the Thirteen Powers draft definition of aggression,⁵⁵ which specified that

[w]hen a State is a victim in its own territory of subversive and/or terrorist acts by irregular, volunteer or armed bands organized or supported by another State, it may take all reasonable and adequate steps to safeguard its existence and its institutions, without having recourse to the right of individual or collective self-defence against the other State under Article 51 of the Charter.

Olivier Corten and Mary Ellen O’Connell also argue that the basis for forcible response to territorial incursions falling short of armed attack is law enforcement. Corten argues that ‘the State has sovereign rights over its territory, authorising it to deploy military forces there without having to appeal to any rule creating an exception whatsoever, whether self-defence or not’.⁵⁶

Tom Ruys disagrees that minimal uses of force within a State’s own territory are justified by law enforcement rights under other legal regimes for land/sea/air, because none of the other legal frameworks cited ‘provide[] a legal basis for forcible action against unlawful territorial incursions by military or police forces of another state’.⁵⁷ He makes the argument that forcible response to small-scale incursions falls within the scope of article 2(4) of the UN Charter but frames the argument in terms of the gravity threshold for a ‘use of force’, rather than in terms of ‘international relations’. He notes that there are theoretical reasons against the idea that there is a gravity threshold for article 2(4), including that armed confrontations between police/military of two States involve ‘international relations’, and the law enforcement paradigm is hierarchical and therefore not suited to equal sovereigns.⁵⁸ According to Ruys, the way States treat these confrontations in their legal discourse shows that even when they use force within their own territory in response to an unlawful incursion, this falls within the jus contra bellum, and therefore, no de minimis gravity threshold exists.⁵⁹

The wording of the text of article 2(4) leaves the interpretation of ‘international relations’ in this respect uncertain. As can be seen from the previous discussion, a use of force by a State in response to small-scale territorial, maritime or aerial incursion raises several intertwined issues, such as the gap between ‘use of force’ and an ‘armed attack’ giving rise to a right of self-defence, the relationship of the jus contra bellum and other applicable legal frameworks such as law of the sea and law enforcement, whether there is a gravity threshold for a ‘use of force’ under article 2(4) and if a hostile or coercive intention is required to enliven article 2(4). But the main legal issue with respect to whether such incidents fall within the scope of the prohibition of the use of force under article 2(4) is the ‘international relations’ element. As Christian Henderson notes, it is not a matter of ‘quantifying the use of force’ in terms of its gravity but rather determining whether ‘international relations’ are engaged, at which point the prohibition of the use of force becomes applicable.⁶⁰ The relationship between ‘international relations’, gravity and intention is discussed further in Chapter 8.

C. Law Enforcement against Foreign Private Actors within or outside Own Territory

There is greater agreement among scholars that law enforcement by a State against foreign private actors within its territory does not usually fall within the scope of article 2(4) as it is not in ‘international relations’.⁶¹ Ruys draws a distinction between the previous example discussed (use of force by a State within its own territory in response to incursions by armed forces of another State) and law enforcement against foreign individuals, merchant vessels and civilian aircraft. He argues this is different to the previous categories because there is a clear legal basis in other legal frameworks such as law of the sea, air law and the UN Basic Principles on the Use of Force and Firearms by Law Enforcement Officials.⁶² Since States must be able to take enforcement measures within their jurisdiction, it does not engage international relations.⁶³ States generally do not invoke use of force language for measures taken under those regimes, even if they go beyond what is lawful.⁶⁴ However, such acts could be a prohibited ‘use of force’ if it ‘directly arises from a dispute between sovereign states’⁶⁵ since law enforcement is hierarchical so it cannot apply between sovereign States and thus international relations are engaged.⁶⁶

However, as discussed in further detail in the case study on excessive or unlawful maritime law enforcement and ‘use of force’ in Chapter 8, the issue is not so straightforward. There is mixed State practice regarding these types of incidents. Whether purported law enforcement against foreign private actors is characterised by States as an unlawful ‘use of force’ in ‘international relations’ under article 2(4) depends on a number of factors, including the gravity of the physical means or effects, intention, nexus of the object of the use of force and another State and if there is a political dispute between the States concerned. Such incidents highlight the complex relationship between these different elements of a prohibited ‘use of force’. This is explored further in Chapter 8.

Conclusion

In sum, it is generally agreed that the following uses of force by a State are usually in its ‘international relations’ and therefore fall within the scope of article 2(4):

• Use of force on the territory of another State or against its extraterritorial sovereign manifestations.

• Use of force to reclaim disputed territory not within de facto control.

• Use of force in violation of international demarcation lines.

• Use of force directly arising from a political dispute between States.

It is also generally accepted that the following uses of force by a State are not in its ‘international relations’ and therefore usually fall outside the scope of article 2(4):

• Use of force by a State within its own territory against its own population.

• Use of force by a State in the exercise of its law enforcement jurisdiction against private foreign actors absent other factors (such as an existing international dispute, excessive force, coercive intent, or lack of sufficient connection to law enforcement jurisdiction).

• Use of force by a State against objects with no close association with another State. For non-State objects/targets that do not have a close association with a State, more will be required to bring the act within the scope of article 2(4), such as the presence of other factors including the gravity of the (potential) effects, a pre-existing dispute between States or a coercive intent against a State. The interplay of the various elements of a ‘use of force’ is discussed in more detail in Chapter 8.

It is controversial whether or under what circumstances the following uses of force by a State are in its ‘international relations’ and therefore fall within the scope of article 2(4):

• Use of force against entities falling short of Statehood.

• Use of force with no nexus to another State but against an international organisation or on terra nullius.

• Use of force within a State’s own territory against small-scale incursions by armed forces of another State.

• Use of force by a State in the exercise of its law enforcement jurisdiction against private foreign actors in the presence of additional factors. This is discussed further in Chapter 6.

‘against the territorial integrity or political independence of any state or in any other manner inconsistent with the Purposes of the United Nations’

Against the Territorial Integrity…

Despite the arguments by some scholars that these terms permit uses of force for a benign purpose,⁶⁷ the second part of article 2(4) was introduced to ensure the prohibition was all-encompassing. This is made clear in the travaux préparatoires.⁶⁸ For instance, at the San Francisco Conference, ‘[t]he Delegate of the United States made it clear that the intention of the authors of the original text was to state in the broadest terms an absolute all-inclusive prohibition; the phrase “or in any other manner” was designed to insure that there should be no loopholes’.⁶⁹ This view was later confirmed during the drafting of the 1970 Friendly Relations Declaration. In the 1964 meeting of the Friendly Relations Special Committee, representatives who commented on the term ‘against the territorial integrity or political independence of any State’ said that this term

did not limit or circumscribe the prohibition on the threat or use of force contained in the same Article. It had been inserted at the United Nations Conference on International Organization, San Francisco, in order to guarantee the territorial integrity and political independence of small and weak States, and was not intended to mean that one State could use force against another on the pretext that it had no designs on the latter’s territorial integrity or political independence but sought to maintain the established constitutional order or to protect a minority, or on any other pretext.⁷⁰

Furthermore, the notion of a permissible use of force for a benign purpose is not supported by State practice, was implicitly rejected by the ICJ⁷¹ and is overwhelmingly rejected by scholars.⁷² Therefore, an otherwise prohibited use of force cannot be legally justified by arguing that it has a limited purpose.

Consent

This wording of article 2(4) does carve out an exclusion from the prohibition in the case of consent, which is not a circumstance precluding wrongfulness but forms an intrinsic part of the primary rule itself.⁷³ According to the International Law Commission:

the consent of the State must be valid in international law, clearly established, really expressed (which precludes merely presumed consent), internationally attributable to the State and anterior to the commission of the act to which it refers.⁷⁴

Conclusion

The factors discussed in this chapter delineate the scope and context of the prohibition of the use of force in article 2(4). In other words, they are fundamental contextual elements which must be present in order for a ‘use of force’ to fall within the scope of article 2(4) and be unlawful under that provision. Accordingly, a ‘use of force’ must take place within the context of the following fundamental requirements to fall within the scope of article 2(4):

• Two or more States: The use of force must be by a State. It is likely that the object/target of the ‘use of force’ must have a sufficient nexus to another State for the ‘use of force’ to be in ‘international relations’ and fall within the scope of article 2(4).

• In international relations.

• ‘Against the territorial integrity or political independence of any state or in any other manner inconsistent with the Purposes of the United Nations’.

From the above analysis of these terms, the following can be concluded regarding acts that fall within and outside the scope of article 2(4):

Uses of force falling outside the scope of article 2(4):

• Use of force by non-UN Member States (although they are bound by the identical customary international law prohibition of the use of force; see Part I).

• Uses of force that are not committed by a State (including indirectly – see discussion of indirect force in Chapter 5) and are not attributable to a State.

• Uses of force not in international relations. It is generally accepted that the following uses of force by a State are not in its ‘international relations’ and therefore usually fall outside the scope of article 2(4):

  1. 1. Use of force by a State within its own territory against its own population.

  2. 2. Use of force by a State in the exercise of its law enforcement jurisdiction against private foreign actors absent other factors (such as an existing international dispute, excessive force, coercive intent or lack of sufficient connection to law enforcement jurisdiction).

• Use of force falling within an exception to the prohibition recognised in the UN Charter, namely, forcible acts in lawful self-defence or validly authorised by the UN Security Council.

• Use of force that is validly consented to.

Uses of force falling within the scope of article 2(4):

• Use of force on the territory of another State or against its extraterritorial sovereign manifestations.

• Use of force to reclaim disputed territory not within de facto control.

• Use of force in violation of international demarcation lines.

• Use of force directly arising from a political dispute between States.

• Use of force for a benign purpose, provided the other requirements of article 2(4) are met. The limited purpose of the use of force does not exclude it from the scope of this provision.

Uses of force for which it is unclear if they fall within scope of article 2(4):

It is controversial whether or under what circumstances the following uses of force by a State are in its ‘international relations’ and therefore fall within the scope of article 2(4):

• Use of force against entities falling short of Statehood.

• Use of force with no nexus to another State, such as against an international organisation or on terra nullius.

• Use of force by a State within its own territory against small-scale incursions by armed forces of another State.

• Use of force by a State in the exercise of its law enforcement jurisdiction against private foreign actors in the presence of other factors (such as an existing international dispute, excessive force, coercive intent or lack of sufficient connection to law enforcement jurisdiction).

5 Elements of ‘Use of Force’ Means

Introduction

Having interpreted the meaning of the contextual elements of article 2(4) of the UN Charter, the following two chapters will apply a process of textual interpretation to the term ‘use of force’ in that article. Chapter 5 will firstly set out subsequent agreements regarding article 2(4), and then examine whether ‘use of force’ means physical/armed force only, and if a particular type of means is required. Chapter 6 will look at the required effects of an unlawful ‘use of force’, and if gravity and intent are required elements of a ‘use of force’ under article 2(4).

Subsequent Agreements Regarding Article 2(4)

Subsequent agreements on the interpretation of the prohibition of the use of force in article 2(4) of the UN Charter include 1970 UN General Assembly (GA) Resolution 2625 (XXV), the Declaration on Principles of International Law concerning Friendly Relations and Co-operation among States in accordance with the Charter of the United Nations (‘Friendly Relations Declaration’); the General Assembly’s 1974 Definition of Aggression,¹ 1987 General Assembly Resolution 42/22 and the 2005 World Summit Outcome Document. These subsequent agreements may contribute to clarifying the meaning of the treaty² and its object and purpose.³ This may be done by:

• determining whether a special meaning was intended by the treaty parties, and if so, what it is;⁴

• after determining the ‘ordinary meaning’ of the terms of a treaty, subsequent agreements and subsequent practice may be consulted to determine ‘whether such conduct confirms or modifies the preliminary result arrived at by the initial textual interpretation or by other means of interpretation’;⁵ and

• contributing, ‘in their interaction with other means of interpretation, to the clarification of the meaning of a treaty. This may result in narrowing, widening, or otherwise determining the range of possible interpretations, including any scope for the exercise of discretion which the treaty accords to the parties.’⁶

There is debate over whether an international organisation’s ‘own practice’ (such as UN General Assembly and UN Security Council resolutions) should be characterised as a form of subsequent agreement and practice under article 31(3) of the Vienna Convention on the Law of Treaties (VCLT).⁷ However, the International Court of Justice (ICJ) has recognised three types of practice that may bear on the interpretation of a constituent instrument of an international organisation (such as the UN Charter):

(a) the subsequent practice of the parties to constituent instruments of international organizations under articles 31 (3) (b) and 32 of the Vienna Convention; (b) the practice of organs of an international organization; (c) a combination of practice of organs of the international organization of subsequent practice of the parties.⁸

The practice of organs of the international organisation may have a different weight with respect to interpretation than the practice of the parties to the constituent instrument themselves.⁹ With respect to (b) the jurisprudence of the ICJ shows that practice of organs of the United Nations such as the General Assembly and the Security Council in the application of the Charter may be relevant as a form of other subsequent practice under article 32 of the VCLT (i.e. as a supplementary means of interpretation), independently of the practice or acceptance of all parties to the UN Charter.¹⁰ Such resolutions will carry more weight when they deal with an area for which the burden of obligation falls on those bodies, such as the Security Council determining what is an act of aggression under article 39 of the Charter. But since that is a political rather than a legal determination, it does not have a direct bearing on the interpretation of the term ‘use of force’ in article 2(4) of the UN Charter.

An example of the practice referred to in (c) is the practice of the UN Security Council and UN General Assembly in the application of the UN Charter that is generally accepted by UN Member States. For example, when a UN Security Council resolution is passed without dissenting votes and is accompanied by the general acceptance of UN Member States, then this may be considered as potentially relevant subsequent conduct confirmed by the practice of the parties demonstrating their agreement regarding the interpretation of the UN Charter under article 31(3)(b) of the VCLT. Nolte observes that the ICJ applied this approach in its Namibia Advisory Opinion, where the Court interpreted the term ‘concurring votes’ in article 27(3) of the UN Charter as including voluntary abstentions ‘primarily by relying on the practice of the organ concerned in combination with the fact that it was then “generally accepted” by member States’.¹¹ Nolte notes that ‘“[g]eneral acceptance” requires “at a minimum” acquiescence’.¹² If the UN General Assembly or UN Security Council pass a resolution with dissenting votes, this may constitute other subsequent practice as a supplementary means of interpretation under article 32 of the VCLT but not as practice establishing the agreement of the parties regarding the interpretation of the UN Charter under article 31(3) of the VCLT.¹³

The decisions of plenary bodies, such as resolutions of the UN General Assembly, may be characterised in certain circumstances as a form of subsequent agreement regarding the interpretation of the constituent instrument.¹⁴ Thus, when a UN General Assembly resolution is passed without dissent (e.g. by acclamation), then this may be considered in certain circumstances as a form of subsequent agreement regarding the interpretation of the UN Charter. The ICJ has considered UN General Assembly resolutions when interpreting provisions of the UN Charter but has made clear that mere adoption is not sufficient and has taken into account the attitudes of States towards such resolutions.¹⁵ Since subsequent agreement between the parties is a means of authentic interpretation of the treaty under article 31(3)(a) of the VCLT because it demonstrates the shared understanding of the parties regarding the interpretation of a treaty, UN General Assembly resolutions may be valued as evidence of such a shared understanding when they are passed without objection (i.e. unanimously or by consensus). This is the case with each of the resolutions discussed below.

1970 Friendly Relations Declaration

The most important and comprehensive subsequent agreement of UN Member States on the interpretation of article 2(4) of the UN Charter is the Friendly Relations Declaration, which was adopted on 24 October 1970 by consensus by the UN General Assembly on the twenty-fifth anniversary of the United Nations. Principle 1 of the Declaration proclaims:

The principle that States shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any State, or in any other manner inconsistent with the purposes of the United Nations.

In the elaboration of this principle, UN Member States took a clear position on the interpretation of article 2(4) with respect to its scope of application to include the following: international boundaries, international lines of demarcation such as armistice lines;¹⁶ forcible acts of reprisal;¹⁷ using force to deprive peoples of the right to self-determination;¹⁸ certain forms of interference in civil strife or terrorist acts in another State¹⁹ and military occupation or territorial acquisition resulting from the threat or use of force.²⁰ (Paragraph 8 of Principle 1 of the Friendly Relations Declaration refers to ‘organizing or encouraging the organization of irregular forces or armed bands, including mercenaries, for incursion into the territory of another State’, however unlike other paragraphs listed under Principle 1, it does not link the legality of this action to a threat or use of force.²¹ Indirect force is discussed in more detail later.) In addition to comprising subsequent agreement of UN Member States on the interpretation of article 2(4), the ICJ relied on the Friendly Relations Declaration in the Nicaragua case as an indication of States’ opinio juris on the existence and content of the customary prohibition of the use of force²² due to its references to ‘all States’,²³ ‘principle’,²⁴ ‘States’, ‘every State’,²⁵ ‘a violation of international law and the Charter’²⁶ and the statement that ‘[t]he principles of the Charter which are embodied in this Declaration constitute basic principles of international law’.²⁷

1974 Definition of Aggression

1974 GA Resolution 3314 annexing the Definition of Aggression was adopted by acclamation (consensus) and was the first time that the international community agreed on a definition of aggression.²⁸ Despite the significance of the 1974 Definition of Aggression, one should be careful about characterising the 1974 Definition as a ‘subsequent agreement’ regarding the interpretation of article 2(4), since it is actually defining aggression as a guideline for the UN Security Council’s political determination. Thomas Bruha argues that because of the politically negotiated nature of the 1974 Definition and its constructive ambiguity, the Definition must be read as a whole and in its context. One cannot extract elements of the ‘definition’ without taking this into account (as Bruha argues the ICJ did in the Nicaragua case). But given the wording in the Definition itself, which refers to uses of force, and the relationship between use of force and aggression – the annex to 1974 GA Resolution 3314 itself notes that ‘aggression is the most serious and dangerous form of the illegal use of force’²⁹ – it is sound to infer a shared agreement or understanding that those acts listed in the Definition constitute ‘use of force’ under article 2(4)).

1987 GA Resolution 42/22

1987 GA Resolution 42/22 (adopted by consensus) was a Declaration on the Enhancement of the Effectiveness of the Principle of Refraining from the Threat or Use of Force in International Relations. This resolution reflects provisions of the 1970 Friendly Relations Declaration regarding non-intervention.³⁰ Like the Friendly Relations Declaration, Resolution 42/22 confirms States’ view that the prohibition of the threat or use of force is universal and binding, referring to the prohibition as a ‘principle’,³¹ holding that ‘[e]very State’ has the duty to comply with the prohibition³² and explicitly stating that ‘[t]he principle of refraining from the threat or use of force in international relations is universal in character and is binding, regardless of each State’s political, economic, social or cultural system or relations of alliance’.³³

2005 World Summit Outcome Document

The 2005 World Summit at the United Nations Headquarters in New York was attended by over 170 Heads of State and Government. This summit produced and adopted by consensus the 2005 World Summit Outcome Document, which is historically and symbolically important as a united stand by UN Member States to reaffirm their commitment to the UN Charter and its purposes and principles in the face of modern challenges to the international order and human security. The principal importance of the 2005 World Summit Outcome Document for our purposes is that in it, the Member States of the UN ‘reaffirm that the relevant provisions of the Charter are sufficient to address the full range of threats to international peace and security’.³⁴ This affirms States’ view of the continued relevance of the collective security framework of the UN Charter. The Outcome Document abridges the wording of article 2(4) in a way that makes it broader, by leaving out reference to ‘against the territorial integrity or political independence of any State’³⁵ and replacing reference to ‘against the Purposes’ of the Charter with the threat or use of force ‘inconsistent with the Charter’.³⁶ The document states³⁷ ‘[w]e rededicate ourselves to … refrain in our international relations from the threat or use of force in any manner inconsistent with the purposes and principles of the United Nations’. Although the earlier parts of the sentence which mention upholding the sovereign equality of States and respecting their territorial integrity and political independence could probably be said to implicitly cover the other parts of article 2(4), it is not clear what, if anything, this shows about the way that States interpret article 2(4).

Listed ‘Uses of Force’ in Subsequent Agreements

The aforementioned UN General Assembly resolutions passed by acclamation (consensus) show that UN Member States have taken a position regarding the interpretation of article 2(4) of the UN Charter with respect to its primary purposes and certain acts which fall within its scope. In particular, the 1970 Friendly Relations Declaration and the 1974 GA Definition of Aggression clearly demonstrate UN Member States’ subsequent agreement that the prohibition of the use of force in article 2(4) includes the following specific acts listed in those documents:

• The ‘use of force to violate the existing international boundaries of another State or as a means of solving international disputes, including territorial disputes and problems concerning frontiers of States’;³⁸

• The ‘use of force to violate international lines of demarcation, such as armistice lines, established by or pursuant to an international agreement to which it is a party or which it is otherwise bound to respect’;³⁹

• Forcible acts of reprisal;⁴⁰

• ‘[A]ny forcible action which deprives peoples referred to in the elaboration of the principle of equal rights and self-determination of their right to self-determination and freedom and independence’;⁴¹

• ‘[M]ilitary occupation resulting from the use of force in contravention of the provisions of the Charter’;⁴²

• Acquisition of the territory of a State resulting from the threat or use of force;⁴³

• ‘The invasion or attack by the armed forces of a State of the territory of another State, or any military occupation, however temporary, resulting from such invasion or attack, or any annexation by the use of force of the territory of another State or part thereof’;⁴⁴

• ‘Bombardment by the armed forces of a State against the territory of another State or the use of any weapons by a State against the territory of another State’;⁴⁵

• ‘The blockade of the ports or coasts of a State by the armed forces of another State’;⁴⁶

• ‘An attack by the armed forces of a State on the land, sea or air forces, or marine and air fleets of another State’;⁴⁷

• ‘The use of armed forces of one State which are within the territory of another State with the agreement of the receiving State, in contravention of the conditions provided for in the agreement or any extension of their presence in such territory beyond the termination of the agreement’.⁴⁸

• The following forms of indirect uses of force are also prohibited:

  • ‘The sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to the acts listed above, or its substantial involvement therein.⁴⁹

  • ‘The action of a State in allowing its territory, which it has placed at the disposal of another State, to be used by that other State for perpetrating an act of aggression against a third State’.⁵⁰

The 1974 Definition of Aggression shows that UN Member States interpret the concept of ‘armed force’ quite broadly. However, these subsequent agreements of UN Member States leave unclear whether article 2(4) prohibits ‘armed’ force only, and what the elements of a prohibited ‘use of force’ are. As there are no statements in the travaux préparatoires that a special meaning of the term ‘use of force’ was intended by the parties under article 31(4) of the VCLT, Chapters 5 and 6 will now examine the ordinary meaning of this term.

Ordinary Meaning

According to article 111 of the UN Charter, the Chinese,⁵¹ French,⁵² Russian,⁵³ English⁵⁴ and Spanish⁵⁵ texts are equally authentic. However, all of these language versions employ the same terms for ‘use of force’ and do not appear to add any further connotations to this term which could assist with shedding light on its interpretation.⁵⁶

According to the Oxford English Dictionary (OED), the noun ‘use’ means ‘[t]he act of putting something to work, or employing or applying a thing, for any (esp. a beneficial or productive) purpose; the fact, state, or condition of being put to work, employed, or applied in this way; utilization or appropriation, esp. in order to achieve an end or pursue one’s purpose’.⁵⁷ The following definition of ‘force’ in the OED most closely corresponds to the way this term is employed in article 2(4):

‘5. a. Physical strength or power exerted upon an object; esp. the use of physical strength to constrain the action of persons; violence or physical coercion’.

‘b. esp. in phr. by force = by employing violence, by violent means, also †under compulsion. †Formerly also through, with, of force’

‘c. spec. in Law: Unlawful violence offered to persons or things’.⁵⁸

This naturally leads to the question of whether the term ‘force’ in article 2(4) is confined to this ‘ordinary meaning’ of physical/violent means only and whether it requires certain types of physical effects.

Means

This section will discuss whether ‘force’ in article 2(4) of the UN Charter is restricted to particular means, namely, if ‘force’ means physical/armed force only, if a weapon must be employed, what is considered a ‘weapon’ and if a release of kinetic energy is required for an act to qualify as a prohibited ‘use of force’.

Physical/Armed Force Only?

The role of article 2(4) in the UN collective security system and its primary objective of the maintenance of international peace and security supports interpreting the term ‘use of force’ as confined to armed/physical force only. This is because forms of non-physical coercion do not directly concern international peace and security but relate more to sovereign equality and the non-intervention principle. Some scholars such as Nikolas Stürchler have argued that the latter (i.e. freedom of choice for States) is not the primary concern of article 2(4). This understanding of article 2(4) excludes non-forcible forms of intervention from the scope of the prohibition of the use of force. This interpretation is further borne out by the following factors: firstly, the choice of the drafters to employ the term ‘use of force’ to overcome the problems associated with the term ‘war’; secondly, references to ‘force’ elsewhere in the UN Charter refer to ‘armed force’; and thirdly, that economic coercion was explicitly rejected by the drafters as a form of ‘force’ falling under article 2(4).

Regarding the choice of term ‘use of force’, as discussed earlier, the historical context of article 2(4) was intended to address the problems of the Covenant of the League of Nations and the Kellogg–Briand Pact, which used the restrictive notion of ‘war’.⁵⁹ References to ‘armed force’ in the UN Charter further support this interpretation of force (referred to later). In particular, preambular paragraph 7 of the Charter refers to armed force, stating one of the goals of the Charter is ‘to ensure, by the acceptance of principles and the institution of methods, that armed force shall not be used, save in the common interest’. With respect to other forms of non-forcible coercion such as economic coercion, the proposal of the Brazilian delegate to the San Francisco conference to include ‘the threat or use of economic measures’ under article 2(4) was rejected by the drafting committee.⁶⁰ The counter-argument, that the explicit reference to ‘armed force’ in other parts of the UN Charter might indicate that the absence of the qualifier ‘armed’ in article 2(4) shows that the drafters did not intend to restrict the term ‘force’ in this way, is less plausible if the latter provision is read in its historical context and in the light of the exclusion of economic coercion. It is then far more persuasive to hold that ‘force’ in article 2(4) only refers to armed force.

The question of whether article 2(4) extends to other forms of coercion was re-opened and subject to extensive debates in the drafting of the Friendly Relations Declaration, but there was ultimately no subsequent agreement overturning the drafter’s clear intent on this point. In each session of the Special Committee,⁶¹ delegates debated this issue and could not reach agreement about the definition of ‘force’ in article 2(4) and, in particular, whether it included armed force only or also other forms of pressure threatening the territorial integrity or political independence of a State, such as economic coercion. Many (mostly newly independent and developing) States were in favour of a broad interpretation of ‘force’ to include not only armed force but also economic, political and other forms of pressure or coercion.⁶² Several proposals included provisions to the effect that the term ‘force’ should be interpreted broadly to cover not only armed force but also economic, political and other forces of pressure,⁶³ particularly those which ‘had the effect of undermining the territorial integrity or political independence of a State’.⁶⁴ Some States in favour of a broad interpretation of the term ‘force’ beyond armed force were nevertheless cautious about including other forms of coercion within the concept ‘in order to avoid enlarging the scope of self-defence’.⁶⁵

Textual arguments in favour of a broad interpretation of ‘force’ included the terms ‘in any other manner’ in article 2(4) of the UN Charter,⁶⁶ and the fact that since other provisions of the UN Charter refer to ‘armed force’ (the Preamble and articles 41, 42, 43, 44 and 46) it is to be presumed that the drafters of the Charter did not intend to limit the term ‘force’ in article 2(4) in this way.⁶⁷ The newly independent States emerging after the process of decolonisation noted that they had not had a chance to shape the interpretation of article 2(4) during the San Francisco Conference and argued that ‘economic and political forms of pressure were sometimes even more dangerous than armed force, particularly for developing countries’.⁶⁸ ‘Many representatives emphasized the need to interpret the term “force” in the light of developments subsequent to the drafting of the Charter.’⁶⁹ Reference was made to the fact that various international declarations, resolutions and treaties had included a broad understanding of ‘force’ and recognised the duty of States to refrain from undue pressure, including economic or other forms of pressure, such as the Bandung, Belgrade and Cairo Declarations, UN General Assembly Resolutions 2131 (xx) and 2160 (xxi), the Charter of the Organization of African Unity and article 51 VCLT and the Declaration on the Prohibition of Military, Political or Economic Coercion adopted by the Vienna Conference on the Law of Treaties.⁷⁰

The third report of the Special Committee sums up ‘the arguments advanced during the debate in favour of a broad interpretation of the term “force” in formulating the principle of the prohibition of the threat or use of force’:

(a) a considerable number of delegations, both in the Special Committee and in the General Assembly, had expressed themselves in favour of a broad interpretation of the term ‘force’; (b) that interpretation was supported by a large sector of opinion and by many writers; (c) that interpretation was recognized in recent international documents such as the Programme for Peace and International Co-operation adopted by the Second Conference of Heads of State or Government of Non-Aligned Countries held at Cairo in 1964; (d) it was necessary to take into account the purposes aimed at in drafting the principle, so that the wording adopted could be made appropriate and useful by taking into account the practices and possibilities of international relations as they existed in reality; (e) it would not be realistic to limit the formulation of the principle to an examination of the provisions of the Charter, in an effort to make a distinction between lex lata and lex ferenda; (f) economic and political forms of pressure were sometimes as dangerous as armed force, particularly for developing countries, new States and peoples under colonial domination, and could accomplish the same illicit results; they constituted a violation of international law and a threat to the maintenance of international peace and co-operation; (g) the existence of international relations based on the free consent of independent sovereign States necessarily implied prohibition both of armed force and of other forms of pressure and coercion; (h) the authors of the Charter, in drafting Article 2, paragraph 4, had used the generic term ‘force’ without any qualification, and consequently a broad interpretation of that term was perfectly compatible with the text of that provision; (i) there was nothing in the travaux préparatoires of the San Francisco Conference to preclude a broad interpretation of ‘force’ in Article 2, paragraph 4, of the Charter; (j) the very fact that the San Francisco Conference had rejected a Brazilian amendment that a reference to economic forms of pressure be added was proof that such a reference was not considered necessary in view of the broad meaning of the term ‘force’ in Article 2, paragraph 4, of the Charter; (k) the notion and conditions of self-defence had not yet been clearly defined, and hence no argument for the exclusion of the various forms of pressure could be based on that notion.⁷¹

On the other hand, many States strongly maintained that ‘force’ within the meaning of article 2(4) was confined to armed force.⁷² Delegates of these States opposed the inclusion of economic, political and other forms of coercion within the scope of article 2(4). The third report of the Special Committee sums up their arguments as follows:

In their turn, those representatives who considered that the term ‘force’ in Article 2, paragraph 4, of the Charter meant only armed force put forward the following arguments: (a) the intention of the authors of the Charter was clearly to limit the term ‘force’ to armed force; (b) the travaux préparatoires of the Charter argued against those who held that, because the term ‘force’ in Article 2, paragraph 4, was not qualified by the adjective ‘armed’, that term should be given a broad interpretation which covered other forms of pressure; (c) the San Francisco Conference rejected a Brazilian amendment designed to broaden the prohibition laid down in Article 2, paragraph 4, by adding the words ‘and the threat or use of economic measures’; (d) the very fact that Brazil had found it necessary to submit its amendment was proof, and the rejection of that amendment conclusive proof of the meaning which should be given to the word ‘force’ in Article 2, paragraph 4, of the Charter; (e) in Article 44 of the Charter the term ‘force’ was also used without any qualification, and there was no doubt that it referred exclusively to armed force; (f) if Article 2, paragraph 4, was analysed in the context of the other provisions of the Charter, the legal conclusion reached was that the term ‘force’ used in that paragraph could be interpreted only to mean armed force; (g) a broad interpretation of the term ‘force’ in Article 2, paragraph 4, of the Charter would completely alter the existing relationship between that Article and the provisions of Chapter VII of the Charter; (h) a broad interpretation of the term ‘force’ in Article 2, paragraph 4 would also imply a broader interpretation of the inherent right of individual or collective self-defence provided for in Article 51 of the Charter, although it was obvious that the protection established in that Article was intended to operate solely in the case of the threat or illegitimate use of force and until such time as the Security Council had taken the necessary steps to maintain international peace and security; (i) a broad interpretation of the term ‘force’ would undermine the integrity of the Charter as a legal instrument – an outcome which could not be accepted on the pretext of progressive development; (j) any attempt to amend the Charter must be made in accordance with the procedure laid down in Article 108; (h) most writers supported a limitative interpretation of the term ‘force’ in Article 2, paragraph 4, of the Charter.⁷³

It was also argued that ‘apart from basic legal objections to the inclusion of economic and political pressures in the definition of force, there was no legally satisfactory definition of economic and political pressures’.⁷⁴

The Friendly Relations Declaration left open the issues of whether a prohibited use of force must be ‘armed’, and whether coercion falls within the scope of the prohibition. Although the Declaration was adopted by acclamation (consensus), seventy-nine delegations made statements on the formulation of the draft declaration at the time of its adoption,⁷⁵ and the Rapporteur of the Sixth Committee, Mr Owada, noted that ‘the text of the declaration should be read in conjunction with the statements made for the record which are included in the relevant part of the summary records of the Sixth Committee, contained in documents A/C.6/SR.1178 to 1184’.⁷⁶ The delegate for the UK, Sir Vincent Evants, drew

attention to the statements summarized in paragraphs 90 to 273 of the Special Committee’s report [A/8018] and in the summary records of the 1178th to 1184th meetings of the Sixth Committee. Individual delegations have made it clear that the acceptance of the declaration by their Governments is subject to the views and positions there expressed and the declaration must consequently be read in conjunction with [those] records.⁷⁷

In particular, the delegate for Nigeria, Mr Shittabey, on behalf of the African Group of States expressed regret over ‘the Committee’s failure to accept the legitimate notion that the expression “force” as employed in the principle of the non-use of force denotes economic and political pressures as well as every kind of armed force’.⁷⁸

In the text of the adopted Declaration, the prohibition of coercion is mentioned twice, firstly in the ninth preambular paragraph which ‘[r]ecall[s] the duty of States to refrain in their international relations from military, political, economic or any other form of coercion aimed against the political independence or territorial integrity of any State’ (emphasis added). The prohibition of coercion is also included with respect to the principle of the duty of non-intervention.⁷⁹ However, the Special Committee reached no ultimate agreement on the issue of whether the prohibition of the use of force includes the prohibition of other forms of coercion.⁸⁰ Some delegations expressed their understanding that ‘[t]he forms of coercion referred to in [preambular paragraph 9] were examples of unlawful forms of the threat or use of force, which was prohibited under the Charter’,⁸¹ and others criticised the fact that ‘the principle concerning the prohibition of political, economic and other forms of coercion’ was ‘covered only in the preamble and not in the operative part’ and considered that it should have been placed in the principle concerning the non-use of force or in the general part of the declaration.⁸²

Ultimately the lack of agreement regarding the definition of ‘force’ with respect to the principle of the non-use of force in the 1970 Friendly Relations Declaration was left unresolved. Accordingly, the 1970 Friendly Relations Declaration does not constitute a subsequent agreement regarding whether or not ‘force’ in article 2(4) refers to physical/armed force only.

Another potential subsequent agreement regarding whether ‘force’ in article 2(4) refers to armed/physical force only is the 1974 Definition of Aggression. Article 1 of the 1974 Definition provides that:

Aggression is the use of armed force by a State against the sovereignty, territorial integrity or political independence of another State, or in any other manner inconsistent with the Charter of the United Nations, as set out in this Definition.⁸³

The introduction of the qualifier ‘armed’ before ‘force’ is the most significant difference to the text of article 2(4).⁸⁴ On first glance, the use of the term ‘armed’ tends to bolster the view that article 2(4) of the UN Charter is directed at armed force only, since that article forms part of the collective security framework of the UN (which is also the context of the Definition of Aggression, for the purposes of providing guidance to the UN Security Council in making a determination under article 39 of the Charter). As discussed, the debates leading up to the Friendly Relations Declaration did not resolve the disagreements between States about whether article 2(4) was confined to armed force only, so the use of the qualifier ‘armed’ in article 1 of the Definition of Aggression could be viewed as a progressive development of international law through the subsequent agreement of the parties regarding the interpretation of article 2(4). Bruha argues that the use of this adjective ‘ended the discussion on “economic” or “ideological” aggression, which had lost much of its significance in the atmosphere of détente looming at that time’.⁸⁵ However, since article 1 is defining aggression, the most serious form of illegal use of force, it does not follow that all illegal uses of force involve armed force. Hence, article 1 of the Definition of Aggression does not unequivocally indicate agreement of the UN Member States regarding the interpretation of article 2(4) as referring to armed force only.⁸⁶

In absence of a subsequent agreement regarding the interpretation of ‘force’ in article 2(4), according to article 32 of the VCLT:

Recourse may be had to supplementary means of interpretation, including the preparatory work of the treaty and the circumstances of its conclusion, in order to confirm the meaning resulting from the application of article 31, or to determine the meaning when the interpretation according to article 31:

1. (a) leaves the meaning ambiguous or obscure.

Accordingly, given the ambiguity of the text of article 2(4) regarding the meaning of ‘force’ and in the absence of a subsequent agreement regarding its interpretation, one should revert to the clear drafter’s intent expressed in San Francisco by the rejection of the Brazilian proposal to include economic coercion, that ‘force’ does not extend to other forms of non-armed/non-physical coercion. Despite some earlier scholarly views,⁸⁷ the position that ‘force’ in article 2(4) includes only armed/physical force and excludes other forms of non-armed coercion is today overwhelmingly supported by scholars.⁸⁸

Weapons

The ICJ has confirmed that article 2(4) does ‘not refer to specific weapons’; articles 2(4), 51 and 42 of the UN Charter ‘apply to any use of force regardless of the weapons employed’.⁸⁹ The ICJ’s view has been affirmed by States in the comment to article 3(b) of the 1974 Definition of Aggression. Article 3(b) 1974 Definition of Aggression lists as an act of aggression: ‘Bombardment by the armed forces of a State against the territory of another State or the use of any weapons by a State against the territory of another State’ (emphasis added). The comment annotated to article 3(b) refers to paragraph 20 of the 1974 GA Special Committee report, which states: ‘the Special Committee agreed that the expression “any weapons” is used without making a distinction between conventional weapons, weapons of mass destruction and any other kind of weapon.’ This makes clear States’ agreement that at least with respect to aggression (and there is no apparent reason it should not extend to all illegal uses of force), the type of weapon used does not affect the lawfulness of the use of force under the jus contra bellum. Although explicitly referring to use of weapons, this term is broadly understood in the annotated comment of the Special Committee. It could also further be argued that as article 3(b) of the 1974 Definition refers to the most serious uses of force (i.e. aggression), it is not necessary that all uses of force (those below the threshold of an act of aggression) should require the employment of a weapon. In any event, the ICJ’s well-known statement does not explicitly state that a weapon must be employed for an act to fall under article 2(4) of the UN Charter, merely that no specific weapon is referred to by article 2(4) and that article 2(4) applies ‘to any use of force regardless of the weapons employed’. Although this does imply that some kind of weapon should be employed, it is not explicitly stated. Apparently, then, the type of weapon is not relevant to whether an act falls under the scope of article 2(4). But this still leaves the question: is the use of a weapon required at all for an act to fall under the prohibition of the use of force in article 2(4), and if so, what is a ‘weapon’?

Is Use of a ‘Weapon’ Required by Article 2(4)?

The question of whether a ‘weapon’ is required by article 2(4) and the definition of ‘weapon’ is particularly relevant to new forms of technology that may be used to commit acts of violence or create a military effect, such as cyber operations (e.g. to attack satellite systems by spoofing telemetry data),⁹⁰ the use of radio frequencies (for jamming and disrupting space systems including satellite signals – discussed further below), or an electromagnetic pulse to damage electrical power and control systems, which could lead to the meltdown of a nuclear reactor.⁹¹ Could these means be considered ‘weapons’, and is the use of a weapon required by article 2(4)? Of course, textually, in article 2(4) there is no mention of weapons. Any requirement for a ‘use of force’ to be effected by a ‘weapon’ must therefore derive from the interpretation of the term ‘use of force’ in that provision. As seen earlier, the ordinary meaning of the term also does not require the use of weapons but merely ‘physical strength or power exerted upon an object; esp. the use of physical strength to constrain the action of persons; violence or physical coercion’ and ‘violent means’.⁹²

What Is a ‘Weapon’?

The answer to whether a ‘use of force’ requires the use of a weapon is made clearer when one considers what a ‘weapon’ is. Some objects (conventional weapons, weapons of mass destruction) are clearly understood to be weapons because they are created, designed and employed to achieve physical damage. But almost anything can achieve physical damage depending on how it is used – so it is either its employed function (which could entail an element of hostile intent) and/or its effect (the harm or damage caused) that determines its character as a ‘weapon’. As Christian Henderson notes, ‘[t]he design of an object as a weapon does not appear to be the determining factor as to whether an action constitutes “force”; rather a weapon is instead “a thing designed or used for inflicting bodily harm or physical damage”’.⁹³ Take the example of an unarmed ballistic missile, such as the Hwasong-12 ballistic missiles that it is believed North Korea launched on 28 August and 15 September 2017 over Hokkaido, Japan.⁹⁴ These appear to be single-stage intermediate-range ballistic missile designed to deliver a payload of a single (conventional or nuclear) warhead.⁹⁵ An intermediate or long-range ballistic missile is a large, high-speed rocket-fuel propelled projectile and so, even unarmed, could be employed as a ‘weapon’. On the other hand, the unarmed missiles themselves are weapon delivery systems that do not actually carry weapons. In other words, an unarmed missile does not belong to the category of conventional weapon, but it has features that allow it to be employed in a way that will achieve the same effect as conventional weapons if it strikes a target (namely, the kinetic energy of the missile will be transferred to the object that it strikes; the friction will ignite the rocket fuel and the missile will explode). Therefore, to be employed as a weapon, an unarmed ballistic missile must have a physical effect, which it would only have by actually striking a target (as opposed to its usual function and effect of describing a ballistic trajectory and landing in water).⁹⁶ Therefore, it is not helpful to speak of ‘weapons’, since in the discussion of what is a ‘weapon’ and whether use of a ‘weapon’ is required, ‘weapons’ is really a signifier standing for other potential requirements for an act to constitute a prohibited use of force under article 2(4), namely, kinetic/physical means, kinetic/physical effects, object of harm, directness of harm and possibly, hostile intent and gravity. These elements will now be considered.

Kinetic/Physical Means

‘Kinetic’ is defined as ‘[p]roducing or causing motion’.⁹⁷ Although the scholarly literature often refers to ‘kinetic force’, it is more accurate to speak of kinetic energy and the transfer or release of kinetic energy to other objects. In conventional weapons, the transfer of kinetic energy occurs when, for example, a bullet that is discharged from a firearm strikes an object and transfers its kinetic energy to that object in the form of kinetic energy and heat, causing physical damage. Since the prohibition of the use of force in article 2(4) undoubtedly covers the use of chemical, biological and nuclear weapons,⁹⁸ a kinetic release of energy is clearly not always required for an act to fall within the scope of the prohibition. Other examples that may fall under the category of forcible acts through employing means other than the release of kinetic energy may include cyber operations;⁹⁹ certain types of interference with space systems such as ‘deliberate interference and “soft kill” techniques against satellites, such as laser dazzling and radio frequency jamming’¹⁰⁰ or spoofing;¹⁰¹ non-conventional weapons such as chemical, biological or nuclear weapons;¹⁰² use of the environment as a weapon¹⁰³ such as diverting a river or spreading fire across a border; and other measures such as contaminating a water source, releasing harmful substances into the air and expulsion of populations.¹⁰⁴

Not all of these examples are necessarily ‘uses of force’ within the meaning of article 2(4); this is merely to illustrate the different means through which it is possible to create physical effects without the kinetic release of energy typically associated with a conventional weapon. One factor that may contribute to the characterisation of some of these non-‘kinetic’ means as a ‘use of force’ is indeed their effect. In sum, physical means are not essential for an act to be characterised as a ‘use of force’ within the meaning of article 2(4) but rather a certain physical effect. Henderson argues that ‘a consideration of the effects of the action takes on a greater importance the further one moves away from what we might consider to be conventional weapons’.¹⁰⁵ This approach also coincides with the Tallinn Manual’s commentary on the definition of the use of force with respect to cyber operations, which sets out indicative factors for whether a cyber operation is a ‘use of force’, focusing on its effects rather than its means.¹⁰⁶

Indirect Use of Force

In addition, with respect to means, the 1970 Friendly Relations Declaration and the 1974 GA Definition of Aggression clearly demonstrate UN Member States’ subsequent agreement that the prohibition of the use of force in article 2(4) includes the following forms of indirect uses of force: ‘The action of a State in allowing its territory, which it has placed at the disposal of another State, to be used by that other State for perpetrating an act of aggression against a third State’;¹⁰⁷ ‘The sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to the acts listed above, or its substantial involvement therein’;¹⁰⁸ and ‘organizing or encouraging the organization of irregular armed forces or armed bands, including mercenaries, for incursion into the territory of another State’.¹⁰⁹ These refer to indirectness of means, rather than of effects, and are discussed further in Chapter 7 (anomalous examples of ‘use of force’).

Conclusion

The above textual analysis of article 2(4) of the UN Charter supports the following conclusions regarding the interpretation of the term ‘use of force’ with respect to its required means:

• Means:

  • Type of force: Article 2(4) refers to physical force and not to non-physical forms of coercion.

  • Type of weapon: It is not necessary that a ‘weapon’ be used; what counts are the (physical) effects.

  • Kinetic energy: It is not required that kinetic energy be released.

  • Physical means: This is not essential, as what counts are the physical effects.

Chapter 6 will explore the required physical effects of a ‘use of force’, as well as whether a particular intention is required.

6 Elements of ‘Use of Force’ Effects, Gravity and Intention

Introduction

This chapter will continue the analysis of the meaning of a ‘use of force’ in article 2(4) of the UN Charter with respect to its required effects, whether there is a gravity threshold for an unlawful use of force, and if a particular intent is required to bring a forcible act within the scope of this provision.

Effects

Building on the previous chapter’s conclusions that ‘force’ in article 2(4) includes physical force (and not non-physical forms of coercion) but that physical means are not necessarily required, this section will show that it is the effects of a ‘use of force’ that are likely to be decisive in its characterisation as such¹ and will analyse the type of effects that are relevant. The following section will evaluate the required nature of the effects of a ‘use of force’ under article 2(4) by discussing if the relevant harm is confined to harm to persons and property only, the required level of directness between the act and its harmful effect, whether the effect should be permanent or if temporary effects suffice and if the effect should actually ensue or if merely potential effects count.

Physical Harm to Persons or Objects

Although it is clear that a forcible act that directly results in physical harm to persons or property (and that meets the other requirements of article 2(4)) will be characterised as a ‘use of force’ under article 2(4),² there is nothing explicit in the text of article 2(4) itself that restricts its scope to physical harm or harm to certain objects. A physical effect may not always be required for an act to constitute a prohibited ‘use of force’.³ However, non-physical effects alone (such as psychological, economic or more abstract forms of harm) are not likely to be legally relevant to the determination of whether an act is a ‘use of force’. During the 1964 meeting of the Friendly Relations Special Committee, ‘[i]t was … pointed out that force could not be exercised in the abstract; when used, it was directed against an international legal entity, including its political organization, population and territory’.⁴ More abstract forms of harm, such as breaking a diplomatic bag⁵ or an unauthorised visit by a Head of State such as the visit by Turkish prime minister Ahmet Davutoglu to visit an Ottoman tomb within the Syrian border on 10 May 2015, which the Syrian government called ‘a clear aggression’,⁶ are unlikely to be widely considered by States as a ‘use of force’ and will fall instead under other legal principles such as the principle of non-intervention.

Christian Henderson states, ‘[i]t may also be that humans are neither killed or injured, nor property damaged or destroyed, when the prohibition is engaged’.⁷ This is due to the emphasis in article 2(4) on territorial integrity and political independence, which does not require harm to persons or property. This is a similar argument to that in Chapter 4 regarding the interpretation of ‘international relations’ and whether uses of force against objects with no nexus to another State fall within the scope of the prohibition. The object or target of the ‘use of force’ can therefore be relevant to both elements: whether the act is in ‘international relations’ and whether it is in fact a ‘use of force’. A forcible act that targets or causes damage to something other than a person or an object is likely to fall outside the scope of the prohibition on both counts.

Directness

The physical effect of a ‘use of force’ must be ‘sufficiently direct’.⁸ The commentary to rule 69 in the Tallinn Manual 2.0 (which defines a ‘use of force’ with respect to cyber operations) suggests that the criterion of directness relates to States’ perception of the military nature of the act, since ‘[i]n armed actions … cause and effect are closely related’.⁹ Directness here refers not to the time elapsed between the use of force and its effect (since in the case of nuclear weapons¹⁰ or cyber operations¹¹ for example, some of the most damaging effects may be delayed) but rather to proximity, that is, the lack of intermediate steps between the action and its result. This means that the use of force should be the proximate cause of harm. This would exclude non-physical ‘force’ such as cyber operations adversely affecting financial markets or the electricity grid. The potential problem with including such acts within the scope of article 2(4) is a lack of sufficient directness of the physical effects, rather than the effects themselves, since clearly interruptions to a power supply of, for instance, a nuclear power plant or a hospital can lead to physical harm to persons and property, or in the case of interruption of power supply or radio signals to a military facility, this could yield a military advantage to the attacking State.

Permanent and Temporary Effects

The text of article 2(4) does not reveal whether the effects of an act must be permanent for it to be characterised as a ‘use of force’. The Tallinn Manual 2.0 does not explicitly list permanence of effects as a criterion for characterising a cyber operation as a ‘use of force’, but the application of its listed criteria (severity, immediacy, directness, invasiveness, measurability of effects, military character, State involvement and presumptive legality) would implicitly include certain cyber operations with only temporary effects, for example, if there is a severe and immediate effect of a military character.¹² Acts which do not cause permanent damage but which could potentially be regarded as a ‘use of force’ include cyber operations such as Denial of Service¹³ and non-kinetic, non-cyber operations that interfere with satellites such as dazzling with lasers, electromagnetic interference for orbital jamming, terrestrial jamming, hijacking, spoofing or scanning.¹⁴ For instance, Kazuto Suzuki notes that

[j]amming space-based or terrestrial receivers of satellite signals by overwhelming them with energy is one way to interfere with space-based communication, GPS signals, and radio frequency sensors. In 2013, for example, North Korea directed a very strong radio frequency signal toward South Korea to disrupt GPS signals. This mass-scale jamming caused huge confusion for air traffic and other vital socioeconomic infrastructures.¹⁵

It is not clear if these acts which cause temporary physical effects would be considered uses of force by States. For instance, in response to further GPS disruption by the DPRK in 2016, South Korea wrote to the UN Security Council that ‘[t]he GPS jamming by DPRK is an act of provocation that poses a threat to the security of the Republic of Korea’¹⁶ but did not invoke the language of article 2(4) of the UN Charter or the right of self-defence under article 51. Uses of force which have only temporary effects are not excluded from a textual interpretation of article 2(4), but it remains to be seen whether subsequent practice of States will demonstrate their agreement regarding such an interpretation. Significant problems of attribution for these types of non-kinetic operations may complicate State’s response and legal characterisation of these acts.

It is interesting to consider whether acts with temporary effects would require a higher gravity threshold (or some other factor) to qualify as a prohibited use of force; in the aforementioned examples of cyber attacks and interference with satellites, it is the gravity (e.g. military nature) of the effects or of the potential effects (e.g. in the case of GPS disruption, potential aviation disasters) that is important rather than the actual direct (temporary) damage/disruption of function. With increasing reliance by States on satellite technology (for instance, the reliance of the United States on satellite technology with respect to its military presence and potential military operations in geographically distant theatres such as the South China Sea¹⁷), it is entirely plausible that even acts with only a temporary effect of disabling or interfering with space systems may in future be treated by States as violating the prohibition of the use of force. Uses of force in outer space are further analysed and discussed in Chapter 8.

Actual or Potential Effects

The wording of article 2(4) of the UN Charter with respect to the threat or use of force is distinguished from article 51 regarding temporality. The phrase ‘if an armed attack occurs’ has been the subject of much controversy and debate as to whether it limits the right of self-defence to after an armed attack ‘occurs’.¹⁸ However, article 2(4) does not mention effects or temporality at all (which is sensible, given that unlike article 51, it does not define conditions for the exercise of a right) but only refers to the terms ‘threat’ and ‘use’ of force. It is therefore textually ambiguous whether any physical effect (i.e. harm) must actually ensue for such acts to fall within the scope of the prohibition of the use of force, or if it is sufficient if there is a potential for physical effects/harm to result.

State practice is mixed and insufficient to draw a definite conclusion regarding whether potential harmful effects would suffice to constitute a prohibited ‘use of force’ under article 2(4). There are some notable examples of merely potential effects being treated as a ‘use of force’ and even an ‘armed attack’, such as the attempted assassination of former US President George Bush in Kuwait in 1993 (discussed in Chapter 8).¹⁹ But of recent alleged State-sponsored assassinations and attempted assassinations involving the use of radioactive (Litvinenko) or chemical weapons (Skripal – analysed in greater detail in Chapter 8, and the assassination of Kim Jong-nam allegedly by North Korean agents in Malaysia on 13 February 2017 with XV nerve agent), article 2(4) was only invoked in relation to the Skripal incident and by only one State (the UK).²⁰ It is therefore unclear if potential effects would suffice to meet the requirements of article 2(4).

It may be that acts with merely potential effects would only meet the threshold of a ‘use of force’ under article 2(4) if they occur in combination with other elements, such as a higher gravity of the potential effects, a clear hostile or coercive intention, or a particularly close connection between another State and the object/target of the act. These considerations may relate to the element of ‘international relations’, since the targeted (attempted) killing of an individual may rise to the level of an international incident due to the use of a prohibited weapon with serious potential effects for the population of the territorial State (as was the case in the attempted assassination of Sergei Skripal with the prohibited nerve agent Novichok). The notion of a combined threshold of elements for an act to constitute a ‘use of force’ and the relationship between the elements of a ‘use of force’ and contextual elements such as ‘international relations’ is explored in more detail in Part III.

Conclusion

It is clear that forcible acts with direct (i.e. sufficiently proximate) physical effects on persons or objects may constitute a ‘use of force’ and fall within the scope of the prohibition of the use of force in article 2(4) if the other requirements of that provision are met. It is textually unclear and remains to be seen through the subsequent practice of States if forcible acts with only temporary effects would fall within the scope of the prohibition in article 2(4). It is similarly legally uncertain if forcible acts with potential but unrealised effects would suffice to constitute a prohibited ‘use of force’ under article 2(4). It is likely that other elements of a ‘use of force’ will be decisive for determining whether such acts meet the definition of this term. The rest of this chapter will consider if there is a requirement for a particular gravity or intention for a prohibited ‘use of force’.

Gravity

It is debated among legal scholars whether there is a ‘de minimis’ gravity threshold for a prohibited use of force under article 2(4) of the UN Charter. The concept of a gravity threshold for prohibited uses of force under article 2(4) of the UN Charter is a hotly contested topic in three respects: firstly, whether there is a lower gravity threshold that a forcible act must reach before it will constitute a ‘use of force’ and fall within the scope of article 2(4); secondly, if there is such a threshold, how high or low it is and how it is to be assessed; and thirdly, the implications of the previous two issues for the ‘gap conundrum’.

This conundrum refers to the gap between the gravity threshold of an unlawful ‘use of force’ under article 2(4) of the UN Charter, and the gravity threshold of an ‘armed attack’ under article 51, which would permit a use of force in self-defence by the victim State. In the Nicaragua case, the International Court of Justice (ICJ) found it ‘necessary to distinguish the most grave forms of the use of force (those constituting an armed attack) from other less grave forms’.²¹ The problem resulting from this approach was pointed out by Judge Jennings in that case:

The original scheme of the United Nations Charter, whereby force would be deployed by the United Nations itself, in accordance with the provisions of Chapter VII of the Charter, has never come into effect. Therefore an essential element in the Charter design is totally missing. In this situation it seems dangerous to define unnecessarily strictly the conditions for lawful self-defence, so as to leave a large area where both a forcible response to force is forbidden, and yet the United Nations employment of force, which was intended to fill that gap, is absent.²²

Clearly then, the gravity threshold for prohibited uses of force is of utmost relevance to the permissibility question, with respect to acts falling below the threshold for an unlawful ‘use of force’ (and hence permissible under jus contra bellum) and with respect to acts above the threshold for a ‘use of force’ but not amounting to an ‘armed attack’ (in respect of which States are not permitted to respond using force under the jus contra bellum). It is a matter of controversy how high the gravity threshold for an ‘armed attack’ is.²³ Notwithstanding where the upper limit of the ‘gap’ between an unlawful ‘use of force’ under article 2(4) and an ‘armed attack’ under article 51 falls, the lower limit of the gap – that is, the lower threshold of a ‘use of force’ – also affects the size of the gap between the two.²⁴ A very low gravity threshold for an unlawful ‘use of force’ increases the size of the ‘gap’ and reduces the range of forcible measures lawfully available to States in their international relations, such as with respect to security measures. Conversely, a relatively high threshold of a prohibited ‘use of force’ reduces the size of the ‘gap’ but is also more permissive, since a wider range of forcible measures would be lawfully available to States before the prohibition in article 2(4) is engaged. Therefore, the view that one takes of a de minimis threshold for ‘use of force’ under article 2(4) is likely to be influenced by one’s position on the aforementioned matters, including one’s position on the appropriate balance between State security and international peace and security, which is liable to be affected by a more permissible regime of potentially escalatory forcible acts. The treatment of these matters in scholarship is analysed next.

Ian Brownlie does not directly discuss the concept of a gravity threshold for article 2(4). He notes that

from the point of view of assessing responsibility ex post facto, the distinction [between a use of force and ‘frontier incidents’] is only relevant in so far as the minor nature of an attack is prima facie evidence of absence of intention to attack, of honest mistake, or simply the limited objectives of an attack. When the justification of self-defence is raised the question becomes one of fact, viz., was the reaction proportionate to the apparent threat.²⁵

According to this position, a lower gravity intensity is an indicator of lack of intention, which is relevant either to whether it is actually an ‘armed attack’ (if intention is a criterion) or to the necessity of using force in self-defence. The relationship between gravity and intention is discussed in Chapter 8.

The more recent discussion by scholars including Olivier Corten,²⁶ Tom Ruys²⁷ and Mary Ellen O’Connell²⁸ frames the question as to whether there is a ‘de minimis’ threshold for a use of force under article 2(4). A note on this terminology: in terms of legal doctrine, ‘de minimis’ is often short for ‘de minimis non curat lex’ – a common law principle available for judges to apply to prevent the strict application of the law to trifles but which does not render the conduct itself lawful.²⁹ ‘The defence of de minimis does not mean that the act is justified; it remains unlawful, but on account of its triviality it goes unpunished.’³⁰ It is an interesting question to consider whether this principle would be applicable in proceedings before the ICJ regarding an article 2(4) violation claim. For violations of the prohibition of the use of force, it is rare that legal claims are brought, and if we limit ourselves to those uses of force that are adjudicated, then we would probably find a much higher gravity threshold for uses of force since States are more likely to bring more grave cases with clearer evidence for adjudication, given the risks, uncertainty and expense of litigation. The term ‘de minimis’ can also be used in the sense employed by Corten, Ruys and O’Connell. The Merriam-Webster dictionary defines ‘de minimis’ as ‘lacking significance or importance: so minor as to merit disregard’.³¹ It is in this latter sense that the term is used in the present discussion.

The three scholars mentioned earlier devote considerable attention to the question of a de minimis threshold and fundamentally disagree on this point. Corten and O’Connell take the position that the prohibition of the use of force contains a de minimis threshold; Ruys posits it does not. Corten argues that ‘it can be concluded that there is a threshold below which the use of force in international relations, while it may be contrary to certain rules of international law, cannot violate article 2(4). The conclusion holds not just on land but also at sea and in the air.’³² On land, he discusses instances of hot pursuit, unlawful arrest and international abductions as police measures falling outside the scope of law enforcement co-operation treaties and not treated as violations of article 2(4).³³ His discussion of police/military measures at sea makes a stronger distinction between police measures (hot pursuit, inspections, prevention of pollution) and the use of inter-State armed force.³⁴ The discussion of measures in the air relates to illegal trespass and shooting down of aeroplanes as a police measure to guarantee air safety or in self-defence of individual aircraft (not the State).³⁵ As to where to place the threshold, Corten argues that the factors determining this are where the action took place (if within the State’s zone of jurisdiction or not, i.e. can it be considered as an enforcement measure within its jurisdiction?) and the context in which the action occurred (whether there is pre-existing inter-State tension or an international dispute).³⁶

According to O’Connell, ‘under the best interpretation, Article 2(4) prohibits any use of armed force or armed force equivalent by a state against another state when the force involved is more than de minimis’.³⁷ She excludes law/maritime enforcement, terrorist attacks by or attributable to States, limited force to rescue hostages, border incursions and serious violations of maritime space including submarines in territorial waters, shooting down planes (e.g. Gulf of Sidra incident) and cyber operations from the scope of article 2(4). ‘[T]he type of force associated with law enforcement does not come within the Article 2(4) prohibition. Shooting across the bow of a ship, shooting at the legs of a person evading arrest and dropping a bomb on an oil tanker to prevent coastal pollution are all examples of such minimal or de minimis armed force.’³⁸ She bases this conclusion on the interpretation of ICJ judgments (namely, the Corfu Channel case, Nicaragua case, Oil Platforms case, the Wall Advisory Opinion and the DRC v Uganda case)³⁹ and examples from State practice, and acknowledges that ‘[t]here is no express authority on the point’.⁴⁰ Examples of State practice that O’Connell provides include the 1981 Gulf of Sidra incident (in which the United States shot down Libyan planes), the 31 March 1999 border incursion by three US soldiers into Serbia, Iranian detention of British sailors in 2007 during the Iraq war, North Korean Navy submarines in Japanese territorial waters, and the 1982 Swedish attempt to bring a submarine to the surface with depth charges and mines. With respect to the latter, she states that ‘[p]lainly the use of depth charges and mines constitutes armed force, but in this case the use did not violate Article 2(4) because it was a minimal use to detain the submarine’.⁴¹ This example implies that it is not the amount or intensity of force or its (potential) effects that are relevant to determining whether the threshold is met but its purpose.

In contrast to Corten and O’Connell, Ruys argues there is no de mininis threshold for a ‘use of force’ under article 2(4). He disagrees with Corten that minimal uses of force within a State’s own territory are justified by law enforcement rights under other legal regimes for land/sea/air, because ‘[n]one of the conventions cited provides a legal basis for forcible action against unlawful territorial incursions by military or police forces of another state’.⁴² He argues that there are theoretical reasons against the idea that there is a gravity threshold for article 2(4): armed confrontations between police/military of two States involve ‘international relations’, and the law enforcement paradigm is hierarchical and therefore not suited to equal sovereigns.⁴³ It also cannot be justified by reference to other legal frameworks. According to Ruys, Corten’s arguments depend heavily on omission, that is, interpreting a failure by States to protest or raise articles 2(4) or 51 as indicating their opinio juris that those provisions do not apply to the incidents in question.

Christian Henderson makes a more nuanced observation about a de minimis gravity threshold, noting ‘the de minimis threshold is normally based upon the distinction between law enforcement actions and uses of force’,⁴⁴ and that this distinction is more complex than whether a certain gravity threshold is met.⁴⁵ He observes that it is not a matter of ‘quantifying the use of force’⁴⁶ in terms of its gravity but rather determining whether ‘international relations’ are engaged, at which point the prohibition of the use of force becomes applicable.⁴⁷ Henderson argues that ‘the gravity of the use of force against such private actors does not by itself determine the applicability of the prohibition … Indeed, it is more a qualitative – state or private – as opposed to quantitative – small- or large-scale – distinction, making a clear de minimis threshold hard to discern’ and that ‘when the “international relations” between states are engaged there is little state practice supportive of a de minimis threshold in the context of incidences involving armed force.’⁴⁸

This author takes a slightly different view to Henderson. With respect to the prohibition of the use of force, gravity of effects is relevant to two separate elements of article 2(4). Firstly, it is relevant to the contextual element of whether the act occurs in ‘international relations’. For example, acts of a higher gravity are more likely to be perceived by States as of a military rather than law enforcement nature and thus as engaging their international relations (discussed in Chapter 8). Also, acts of higher gravity may evince a hostile or coercive intention (discussed in the following section) with respect to another State and thus engage ‘international relations’ on that basis. The second point of relevance of gravity is to the question of whether the act constitutes a ‘use of force’ at all. Since, as Ruys convincingly argues, State practice makes clear that when ‘international relations’ are engaged, ‘any actual armed confrontation between two states, even if small-scale or localized, comes within the ambit of the jus ad bellum’,⁴⁹ it does appear that there is no de minimis gravity threshold. However, gravity of effects remains a relevant factor in the assessment of whether an act constitutes a ‘use of force’. As the preceding discussion of effects noted, gravity may be an especially relevant factor in converting some types of acts into a ‘use of force’, such as when the act has only temporary effects, or merely potential but unrealised effects. The relationship between these different elements of a ‘use of force’ and the contextual elements of article 2(4) such as ‘international relations’ is the subject of Chapter 8 and is explored through case studies of subsequent State practice.

A further consideration is that the (perceived) gravity of a use of force is strongly influenced by the domain in which it takes place, namely, land, sea, air or outer space. These domains differ in the following relevant ways: firstly, the type of acts that are possible or frequent in those domains (e.g. interdiction of vessels, satellite interference); secondly, the perceived or actual security threat to the State (i.e. potential effects and security interests at stake); and, thirdly, the legal rights and obligations of States under other applicable legal frameworks (e.g. different maritime spaces under the law of the sea). Within several of these domains, it may be relevant whether the forcible act took place vis-a-vis the States concerned:

• within a State’s own territory (land/air/sea – internal waters, territorial waters);

• within territory of another State (land/air/sea);

• within territory governed by a special regime allocating rights and duties between States (Exclusive Economic Zone and contiguous zone, international straits, archipelagic waters, etc);

• within a space beyond the territory of any State (international airspace/high seas/Antarctica/outer space, the Moon and other celestial bodies);

• on movable objects: ships, submarines, aircraft, spacecraft, satellites and other man-made space objects registered to a State; or

• on extra-territorial manifestations of the State: e.g., embassies and diplomatic premises and warships.

As noted by Judge Alejandro Alvarez in the Corfu Channel case:

Sovereignty confers rights upon States and imposes obligations on them. These rights are not the same and are not exercised in the same way in every sphere of international law. I have in mind the four traditional spheres – terrestrial, maritime, fluvial and lacustrine – to which must be added three new ones – aerial, polar and floating (floating islands). The violation of these rights is not of equal gravity in all these different spheres.⁵⁰

Conclusion

Ultimately, the controversy regarding the gravity threshold of a ‘use of force’ under article 2(4) is not solved by the text of that provision, which neither specifies nor excludes a gravity threshold for an act to constitute a ‘use of force’ and therefore fall within the scope of the prohibition. Accordingly, the matter is uncertain at the legal of textual interpretation. The issue of whether article 2(4) has a de minimis gravity threshold depends on the subsequent practice of States in their application of this provision. The analysis of subsequent practice by other scholars in relation to this issue, especially by Corten and Ruys, demonstrates that the interpretation of this practice and the conclusion of whether a ‘use of force’ has a gravity threshold is strongly influenced by the position one takes regarding the legal significance of silence and inaction. This author finds Ruys’ analysis of State practice on this matter convincing and agrees that there is no de minimis gravity threshold as such for a prohibited ‘use of force’ under article 2(4). However, this section has argued that gravity is nonetheless a relevant factor to an assessment of whether an act violates article 2(4) on two bases: firstly, as a factor relevant to whether the act occurs in ‘international relations’ (e.g. as an indicator of intention), and, secondly, as a relevant factor to whether the act constitutes a ‘use of force’ for acts that may otherwise not meet the threshold of the definition, for instance, because its effects are temporary or only potential. The complex relationship between ‘international relations’ and of gravity and intention as elements of a ‘use of force’ is illustrated in further detail in Part III.

Intention

Although intention is regarded by some as a requirement for an ‘armed attack’ under article 51 of the UN Charter,⁵¹ this is disputed, since hostile intent is perhaps better considered in terms of whether a use of force in self-defence is necessary.⁵² The picture is even less clear when it comes to a ‘use of force’ under article 2(4). According to the commentary to the International Law Commission (ILC) Draft Articles on State Responsibility, intention is not a necessary requirement for an act to be internationally wrongful; whether intention is necessary depends on the obligation in question.⁵³ It is not clear from the text of article 2(4) if a prohibited ‘use of force’ entails a particular intention. Whether a particular intention is an element of a prohibited ‘use of force’ under article 2(4) is illuminated by examining the other prohibition in that provision which is more clearly associated with coercion, namely, the ‘threat … of force’. If prohibited threats to use force require a coercive intent and the two prohibitions of threats and use of force are coupled, this would indicate that the latter also requires a coercive intent. This section will firstly examine these questions and then analyse if and what kind of intention may be required for an act to constitute prohibited force, and problems of evidence and proof.

Intention and ‘Threat … of Force’

The meaning of prohibited threats of force in article 2(4), similar to its counterpart of prohibited force, has received relatively little treatment in scholarship⁵⁴ and jurisprudence.⁵⁵ The ICJ’s jurisprudence does not make clear whether coercion is required for an unlawful ‘threat of force’. The Corfu Channel case could be interpreted this way, since in that case the ICJ held that the UK was entitled to make threats if the purpose was to deter Albania from firing on its ships, but it was not entitled to make a demonstration of force ‘for the purpose of exercising political pressure’ on Albania.⁵⁶ However, this case is of little precedential value in determining the meaning of article 2(4), because it is so ambiguous and has been cited in support of diametrically opposed positions.⁵⁷

The two main scholars who have examined the meaning of threats of force in article 2(4), Nikolas Stürchler⁵⁸ and Romana Sadurska, have different views on whether coercion is a necessary element of prohibited threats. Stürchler argues that coercion is not an essential element of a prohibited ‘threat of force’. Despite article 2(7) of the Charter, which guarantees States freedom of choice, the primary purpose of the UN Charter is the prevention of war rather than freedom of choice (i.e. freedom from coercion).⁵⁹ He gives the example of a war-mongering State that is no longer trying to ensure compliance with anything – a threat or use of force by that State is thus not coercive (no compliance is sought), but it is still unlawful.⁶⁰ But coercion could still be a ‘strong indicator’⁶¹ in determining the unlawfulness of threats under article 2(4), in which case what distinguishes unlawful threats from unlawful intervention is the ‘military dimension’.⁶² The relevance of coercion as a criterion is in showing ‘that the threat of force is not, when properly understood, the mere preparation for the use of force.’⁶³ Rather, threats can be ends in themselves by ensuring compliance at a much lower cost than an actual use of force. Sadurska agrees that the prohibition of threats of force is aimed at international security rather than the individual liberty of each State from external pressure⁶⁴ but takes as her starting point a concept of threat of force as ‘a form of coercion because it aims at the deliberate and drastic restriction or suppression by one actor of the choices of another’.⁶⁵ Hence, it is uncertain whether coercion constitutes an essential ingredient of a prohibited threat of force, although, at the very least, it may be considered a strong indicator of unlawfulness.

Relationship of ‘Threat’ to ‘Use’ of Force

Even if coercion were a necessary element of a prohibited threat of force, it is unclear what consequence this would have for whether coercion is required for a prohibited use of force. This depends on the relationship between threats and uses of force under article 2(4) (whether they are coupled or uncoupled), and whether the two prohibitions of ‘threat’ and ‘use’ of force are regarded as a continuum or as separate but related prohibitions (and therefore distinct concepts). Stürchler identifies three possibilities for the direct relationship between ‘threat’ and ‘use’ of force in article 2(4).⁶⁶ The two (minority) possibilities for the relationship between the prohibition of the threat of force and the use of force both hold that the two prohibitions are uncoupled. These two related though opposed possibilities are predicated on differing models, namely, the spiral and deterrence models of international conflict.⁶⁷ The first ‘uncoupled’ option emphasises that threats can spiral into armed conflict and takes the position that threats are unlawful under any circumstances, even if the force threatened would be lawful, such as the threat to use force in self-defence.⁶⁸ The second option holds that threats can serve peace through deterrence and are more justifiable than uses of force since the consequences are lower and threats are more likely than actual uses of force to be proportionate. Therefore, according to this view, as propounded by Sadurska, threats to use force may be lawful even if the force threatened would be unlawful.⁶⁹ The basic idea is that the rationale behind prohibiting threats or use of force differs in its application to those two concepts, since uses of force are destabilising to international peace and security, whereas threats of force do not always have destructive effects (lower gravity) and can sometimes help maintain international security (purposes of UN Charter).⁷⁰ This asymmetry theory has been critiqued as inconsistent with the UN Charter drafters’ intention and with State practice,⁷¹ although Stürchler cogently argues that ‘States rely on these themes [of the deterrence and spiral models of conflict] in order to judge the permissibility or otherwise of countervailing threats’, especially in the context of protracted conflict.⁷² The final (and mainstream) position is that threats are coupled to a use of force so that if the force threatened would be unlawful, the threat is unlawful.⁷³ ICJ jurisprudence and State practice tend to confirm that threats and use of force are coupled and that the threat of force is justified in self-defence.⁷⁴ According to the ICJ in its Nuclear Weapons Advisory Opinion, ‘the notions of “threat” and “use” of force … stand together in the sense that if the use of force itself in a given case is illegal – for whatever reason – the threat to use such force will likewise be illegal’.⁷⁵

The ICJ’s above statement in the Nuclear Weapons Advisory Opinion also appears to interpret threats and uses of force as a continuum: concepts that share the same elements but are differentiated merely in form (with threats as a potential but as yet unrealised ‘use’ of force). Stürchler takes a different view and asserts that threats of force are a separate though related prohibition to the prohibition of the use of force. According to Stürchler, threats do not fit easily into a forcible intervention –> use of force continuum since threats can be broken down along two axes of method (words/actions) and motivation (compellence/deterrence); that is, not all threats are forcible since they may but do not necessarily involve demonstrations of force, and some uses of force are better characterised as threats of further force.⁷⁶ Furthermore, threats may but do not necessarily involve coercion and can be ends in themselves and not a prelude to a use of force. Stürchler concludes: ‘The dichotomy of threat and use, as suggested by the formulation of article 2(4), is misleading. Although the threat and use of force are conceptually different, that does not mean that they exclude each other in the field.’⁷⁷ If one adopts the view of the ICJ that threats and uses of force are coupled and form a continuum, then if ‘threat of force’ requires coercive intent, the same holds true for ‘use of force’. However, different views may be taken on each of these issues with respect to the ‘threat of force’, and the text of article 2(4) remains open to different interpretations on this point.

Intention and ‘Use of Force’

There is a similar lack of consensus among scholars focusing on the meaning of ‘use of force’ as to whether intention is an element of a prohibited ‘use of force’. Ian Brownlie argues that intention is not part of the criteria of prohibited use of force and believes this is a good thing, because to hold otherwise would create unacceptable loopholes in the prohibition.⁷⁸ In contrast to Brownlie, Corten argues that ‘[s]uch an intention appears to be an essential characteristic of the use of force under the Charter’.⁷⁹ Henderson also argues that ‘it is clear that there must be an intention to use force, or an animus belligerandi, in order to breach the prohibition of the threat or use of force’.⁸⁰ Ruys notes that ‘state practice reveals that, when faced with territorial incursions ostensibly or allegedly lacking hostile intent, territorial states often refrain from invoking the language of Article 2(4) or 51’.⁸¹ However, he notes that this does not necessarily reflect a legal conviction and that State responsibility is ‘objective’ so does not require intent unless this forms part of the primary rule.⁸² For small-scale incursions, Ruys states that ‘the key is to determine whether they reflect a hostile intent’ to exclude unintentional or harmless acts.⁸³ With respect to law enforcement within a State’s own territory, Ruys argues that manifest hostile intent is sufficient but not necessary for an act to be a ‘use of force’.⁸⁴

Adding to the lack of clarity is that the scholarly literature is not consistent in the use of this term. A hostile intention may refer to an intended action, intended effects or intended coercion. The difference is significant, because it may capture or exclude different categories of forcible acts. To speak of a mental state of an abstract entity such as a State is a fiction, since States have neither a physical body nor mind and can only act indirectly through individuals. Therefore, a mental element attaching to a State obligation (in this case, to refrain from the ‘use of force’ under article 2(4) of the UN Charter) would be satisfied if it is held by a person whose conduct is attributable to the State under the rules set out in the ILC Articles on State Responsibility relating to attribution.⁸⁵ This could be either the individual using force (e.g. a soldier) or directing the use of force (a military commander or government official). With respect to what is meant by a hostile intention, at the very least, it requires ‘that the State in question is aware it is undertaking an action against another State’.⁸⁶

Intended Action

If a hostile intent means intended action, this would rule out forcible acts that are accidental, but it would not necessarily rule out mistaken acts. Ruys argues that State practice shows there is a distinction between incursions that are accidental and ‘the accidental projection of armed force … across a border’ (e.g. shots or shells fired). ‘In the latter scenario … the territorial state is not necessarily precluded from characterizing the act as a use of force’.⁸⁷ The text of article 2(4) strongly indicates that an intended action is required, through the italicised words: ‘All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.’

Intended Effect

If a hostile intent means an intention to have a certain effect, this could rule out mistake, since the action itself is intended but the target, effect or the factual basis may be mistaken. Corten notes that use of force in error was raised in the travaux préparatoires of the 1974 GA Definition of Aggression and ‘States unanimously excluded the possibility of characterising an act committed by mistake as an aggression’.⁸⁸ However, as Corten acknowledges, a problem with this analysis is that although intention may be a requirement for an act of aggression, a use of force may not necessarily amount to aggression. He goes on to argue that ‘a review of practice as a whole allows us to affirm that States consider an act, even of a military type, committed by mistake, does not constitute an aggression or even a use of force by one State against another contrary to article 2(4)’.⁸⁹ Such practice includes instances of aerial incursion, incursion by South African police into Basutoland (then a British colony) on 26 August 1961, a mistaken attack by UAR on the Federation of South Arabia due to ‘pilot’s error’ on 15 July 1965, and a mistaken firing of five shells by Swiss artillery onto the territory of Liechtenstein during a military exercise on 14 October 1968.⁹⁰ In none of these cases did States invoke article 2(4) (although this does not exclude the characterisation of these incidents as internationally wrongful on other legal grounds, such as a violation of sovereignty).

Defining a hostile intent for the purposes of article 2(4) as an intention to produce a particular effect could also rule out deliberate acts with no intention to have a forcible effect within another State. For example, Corten notes that

[d]uring the discussion before the adoption of General Assembly resolution 3314 (XXIX), Iraq’s representative raised the case of a regiment that crosses a State border, knowingly and without authorisation, to go sunbathing on a beach. No State characterised such a hypothesis as a use of force in the debates in the General Assembly, whether in the Sixth Commission or in the special committee on the definition of aggression.⁹¹

Corten contrasts this situation with deliberate acts which do not directly target the territorial State but which nevertheless use force, for example, targeted operations such as rescue of nationals abroad and targeted killing. He argues that in respect of targeted operations,

[i]f the intervening State’s objective is not to challenge another State, and if consequently it uses very limited military means, article 2(4) will not be invoked (as in the Rainbow Warrior or 1990 Liberia precedents). If the military action is against another State that supposedly supports ‘terrorists’ or threatens nationals of the intervening State, the action will involve the rules on the prohibition of the use of force (as in the Mayaguez or Entebbe precedents).⁹²

The fundamental point is that:

For the prohibition of the use of force to be applicable, it is necessary but sufficient for a State to decide to take action that it knows will involve defying another State, whether its central government, its agents, its population, its territory or its infrastructure. … If such an intention is found, article 2(4) will be applicable, regardless of any more general motive for the intervention.⁹³

This point relates to a coercive intent and is addressed in the following section.

With respect to intended effects, there is nothing in the text of article 2(4) to indicate or to exclude this as necessary for a prohibited ‘use of force’. (There is also a question of whether the notion of hostile intent would require an intended harmful effect or if some other mental State would suffice, such as negligence, recklessness or reasonable foreseeability. But this is going even further beyond the text.) It will therefore depend upon the subsequent practice of States in their application of article 2(4). As set out earlier, there is practice indicating that States do not usually invoke article 2(4) in cases of mistake of fact.

Coercive Intent

Finally, hostile intent may refer to a coercive intent. Corten argues that ‘[t]he only intention to be considered is that of forcing the will of another State’.⁹⁴ Corten sees this requirement as so essential that ‘when a State takes even limited military measures and admits that such measures are part of a policy conducted against one State, there is no doubt that article 2(4) is applicable’.⁹⁵ The position that coercive intent is a requirement for a prohibited use of force finds some support in a textual interpretation of article 2(4), due to the relationship between the prohibition of threats and uses of force (as discussed earlier); the relationship of the non-intervention principle and the principle of the non-use of force; and the object and purpose of the prohibition of the use of force in article 2(4).

The principle of non-intervention is found in customary international law and is a ‘corollary of the sovereign equality of States’ set out in article 2(1) of the UN Charter.⁹⁶ In the Nicaragua case, the ICJ defined the content of the principle of non-intervention (as it related to the dispute in question) as follows:

the principle forbids all States or groups of States to intervene directly or indirectly in internal or external affairs of other States. A prohibited intervention must accordingly be one bearing on matters in which each State is permitted, by the principle of State sovereignty, to decide freely. One of these is the choice of a political, economic, social and cultural system, and the formulation of foreign policy. Intervention is wrongful when it uses methods of coercion in regard to such choices, which must remain free ones.⁹⁷

Henderson argues that intention is necessary for a breach of the prohibition of the use of force in article 2(4) because ‘[f]orce … is a particular kind of intervention’.⁹⁸ He follows the ICJ’s approach in Nicaragua and views a ‘use of force’ as ‘a more specific form of intervention’ ‘involving physical coercion’.⁹⁹ This is yet another continuum approach; since intervention requires coercion and a use of force is a form of intervention, a use of force also requires coercion. However, it is not clear from the judgment whether a use of force must always be coercive. Just as an unlawful intervention can be forcible or non-forcible, it is arguable that a prohibited use of force can violate the principle of non-intervention or not. In other words, not all violations of the prohibition of the use of force in article 2(4) will necessarily comprise violations of the principle of non-intervention. For example, a non-combatant evacuation of nationals from a generalised situation of violence or civil unrest abroad is not aimed at coercing a choice ‘on matters in which each State is permitted, by the principle of State sovereignty, to decide freely’ such as ‘the choice of a political, economic, social and cultural system, and the formulation of foreign policy’¹⁰⁰ but may nevertheless constitute a use of force in the territory of another State.

The final argument that a ‘use of force’ requires a coercive intent is based on the object and purpose of article 2(4). As discussed in Chapter 4, the main objects of article 2(4) are protecting State sovereignty (also protected by the non-intervention principle) and the maintenance of international peace and security. The protection of State sovereignty by article 2(4) is further supported by the principles of sovereign equality and non-intervention set out in articles 2(3) and 2(7) (although it is important to note that article 2(7) does not actually prohibit intervention by States in the internal affairs of other States; as mentioned earlier, the non-intervention principle is found in customary international law and not directly in the UN Charter itself). Considering this purpose behind the prohibition in article 2(4), it would make sense to interpret it as prohibiting conduct that is employed to bring about coercion/interference with the sovereign equality of States.

With respect to the second object and purpose of article 2(4) – to maintain international peace and security – one of the propositions Stürchler tests is that article 2(4) can be read together with article 2(3) to imply a positive obligation to achieve peaceful settlement of disputes without recourse to threats to use force.¹⁰¹ This idea could be applied to the interpretation of a ‘use of force’ in article 2(4) to argue that the prohibition of the use of force is directed towards uses of force in contradistinction to the obligation of peaceful settlement of disputes (which Stürchler notes was recognised by the ICJ as a positive obligation in the North Sea Continental Shelf cases¹⁰²). In other words, it could be argued that only those minimal uses of force that are used as a tool for foreign policy (i.e. accompanied or motivated by an element of coercion) would violate the prohibition. This would also reflect the notion of ‘use of force’ as a broader concept but in many ways a continuation of the old concept of ‘war’ from the preceding treaty, the Kellogg–Briand Pact, which condemns ‘recourse to war for the solution of international controversies’ and embodies its renunciation ‘as an instrument of national policy’.¹⁰³ The Principle set out in article 2(3) of the UN Charter that ‘[a]ll Members shall settle their international disputes by peaceful means in such a manner that international peace and security, and justice, are not endangered’ is a continuation of this aim to prevent the settlement of international disputes by force.¹⁰⁴ This also connects to the term ‘international relations’ in article 2(4);¹⁰⁵ as Chapter 8 will show, the elements of ‘international relations’, gravity and intention are interrelated.

A requirement of coercive intent may also play a role in determining whether an act falls within the scope of the jus contra bellum or another legal framework applicable within a particular domain, such as law of the sea. With respect to the location of the forcible act, as noted earlier in the discussion about gravity, the domain in which it occurs may impact on the legal characterisation of the act due to the sovereign rights and applicable legal framework within that space as well as the different nature of the perceived security threat. Measures which may be governed by another legal framework (such as the exercise of law enforcement jurisdiction at sea) could fall within or outside the scope of article 2(4) of the UN Charter, depending on a number of factors – including the element of a hostile or coercive intention vis-à-vis another State (in this case, the flag State of the vessel) – which may bring an act of purported maritime law enforcement within the realm of ‘international relations’ and thus a prohibited ‘use of force’ under article 2(4) of the UN Charter. Interestingly, legal clarity over certain types of acts as definitely constituting unlawful uses of force may relate to intention. For example, as discussed in Chapter 5, the listed acts of aggression in the 1974 GA Definition of Aggression constitute a ‘subsequent agreement’ by UN Member States that those acts are unlawful ‘uses of force’ in violation of article 2(4). Thus, if a State commits one of these acts, it is highly likely that it had a hostile intent, since the act is unambiguously unlawful.

Evidence of Hostile Intent

If a hostile intent (however defined) is required for an act to be an unlawful ‘use of force’ under article 2(4), this raises questions of what kind of evidence counts and the required standard of proof. A problem with hostile intent is that intention is a subjective standard requiring a particular mental state, as opposed to an objective standard in which only the action or omission is relevant for the prohibition to be engaged.¹⁰⁶ The problem of subjectivity is addressed by Ruys by adding the term ‘manifest’ to allow for an objective assessment of intention behind the act.¹⁰⁷ But on another view, manifest hostile intent relates to an ‘armed attack’, for example, to determine the necessity of using force in response.

Indicators that have been suggested for a hostile intent include ‘the gravity or magnitude of the attack’;¹⁰⁸ for less grave acts, States take into account other factors to determine intent, such as geopolitical context, repeated nature, location, nature of units, and specific indications related to weapons being fired up.¹⁰⁹ Corten provides six criteria that indicate gravity and intention (which in his view are interrelated): (1) where the act was carried out, (2) the context, (3) who decided on it and who conducted it, (4) the target, (5) whether ‘the military operation [has] given rise to confrontation between the agents of two States’ and (6) ‘the scope of the means implemented by the intervening State’.¹¹⁰ The Independent International Fact-Finding Mission on the Conflict in Georgia also set out indicators of hostile intent:

According to State practice … not all militarised acts amount to a demonstration of force and thus to a violation of Art. 2(4) of the UN Charter. Many are routine missions devoid of any hostile intent and are meaningless in the absence of a sizeable dispute. But as soon as they are non-routine, suspiciously timed, scaled up, intensified, geographically proximate, staged in the exact mode of a potential military clash, and easily attributable to a foreign-policy message, the hostile intent is considered present and the demonstration of force manifest.¹¹¹

There thus appears to be a connection between these objective indicators of a subjective hostile intent and the elements of gravity and international relations. The relationship between these elements is explored further in Part III.

Conclusion

Ultimately, whether or not intention is required for a prohibited use of force under article 2(4) cannot be definitively resolved at the level of textual analysis. It is possible that hostile intent is an indicative factor that can turn a forcible act that would otherwise not meet various criteria, such as gravity or if the harm is only potential but unrealised, into a ‘use of force’. This discussion about the interrelationship between different elements of a ‘use of force’ (including the relationship between intention, gravity and international relations with respect to maritime law enforcement versus ‘use of force’) is continued in Part III.

Conclusion

The above textual analysis of article 2(4) of the UN Charter supports the following conclusions regarding the interpretation of the term ‘use of force’:

• Effects:

  • Physical effects: Usually required but with some notable exceptions (discussed in Chapter 7).

  • Object/target: There is nothing explicit in the text of article 2(4) itself that restricts its scope to certain objects of harm, i.e. harm to physical property or persons. However, abstract forms of harm are probably excluded from the scope of an unlawful ‘use of force’.

  • Directness: The relevant harmful effects must have sufficient proximity to the application of force. This refers to the intermediate steps between the act and its result, not how long it takes for the harm to manifest.

  • Permanent versus temporary: The text of article 2(4) is not conclusive on this point. More State practice is required to determine whether it will reveal their agreement regarding this interpretation.

  • Actual versus potential: It is textually ambiguous whether any physical effect (i.e. harm) must actually ensue from such acts for them to fall within the scope of the prohibition, or if it is sufficient if there is merely a potential for physical effects/harm to result.

• Gravity of effects: Although this work takes the position that there is no de minimis gravity threshold for a ‘use of force’ under article 2(4), gravity is relevant to the contextual element of ‘international relations’ (e.g. as an indicator of intention), and is a relevant factor to whether the act constitutes a ‘use of force’ for acts that may otherwise not meet the required threshold of the definition, for instance, because its effects are temporary, or only potential.

• Hostile intent: The text of article 2(4) strongly indicates that at the very least, an intended action is required. The text does not explicitly require or exclude an intended effect, although State practice indicates that mistaken forcible acts are usually not treated as violating the prohibition of the use of force. There is textual support for the position that a coercive intent is required under article 2(4), due to the relationship between the prohibition of threats and uses of force, the relationship of the non-intervention principle and the principle of the non-use of force, and the object and purpose of the prohibition of the use of force in article 2(4). However, such textual support is not definitive and the argument can be made both ways. It is possible that hostile intent is an indicative factor that can turn a forcible act that would otherwise not meet various criteria (such as gravity or if the harm is only potential but unrealised) into a ‘use of force’.

However, it is clear that some ‘uses of force’ that are widely accepted as such; for instance an unopposed invasion or military occupation does not contain some of the elements identified above, particularly physical means or a physical effect. These examples challenge the conventional understanding of a prohibited ‘use of force’ as displaying the elements identified in this and the preceding chapter. How are these accepted forms of ‘use of force’ to be reconciled with the above analysis? This is the subject of Part III.