What We Owe to Ukrainians: A Moral Perspective on Nuclear Coercion and Military Intervention

Abstract

Ukraine's war of self-defense against Russia is one of the clearest examples of a nation fighting a just war in recent history. Ukraine is clearly entitled to defend itself, and Russia is clearly obligated to cease hostilities, withdraw troops, and make repair. In light of this, some of the most salient moral questions related to Russia's war of aggression in Ukraine involve the international community; namely, what moral duties it has toward Ukraine, especially in light of Russia's extreme and pervasive human rights abuses. The first section of the essay argues that there is a pro tanto moral duty to intervene militarily in Ukraine to stop Russian human rights abuses and ensure that Ukraine achieves a military victory. This duty is grounded in duties of rescue, promissory obligations, and reliance obligations, as well as duties to nations’ own citizens and to the international community. The second section of the essay argues that the most relevant consideration in determining whether there is an all-things-considered duty for the international community to intervene militarily in Ukraine is Russia's nuclear coercion and the associated risk of nuclear war. This section highlights the nuclear risks involved in compliance with Russian nuclear coercion, which I argue have been neglected in prominent discussions. The moral stakes involved in this determination are very high, and succumbing to Russian nuclear coercion in the face of massive human rights violations would set a dangerous precedent. Any course of action should be guided by a thorough analysis of all the risks involved, both nuclear and moral.

There is no question that Russia is waging an illegal and immoral war of aggression in Ukraine, nor is there any question that Ukraine has a right to military self-defense. Indeed, Ukraine's self-defense against Russia may be one of the clearest examples of a nation fighting a just war in accordance with jus ad bellum principles.¹ Because of Ukraine's clear right to resist Russian aggression and Russia's clear duty to cease its war and withdraw its troops, the most salient moral questions related to the war involve the international community. The outcome of the war, Russia's profound rights abuses, and its impact on the international community all bear on these questions. If we are interested in the morality of the war in Ukraine, we should ask what moral duties the international community (both individual states and collectives within it) has in general and what specific duties it has toward Ukraine, and what considerations bear upon those duties. I argue two points: the first is that there is a pro tanto duty to intervene militarily in Ukraine to stop Russian human rights abuses and ensure that Ukraine achieves a military victory and sustainable territorial integrity, such that Ukraine's 1991 borders are restored and can be maintained without ongoing armed conflict. The second is that the most relevant moral consideration in determining whether there is an all-things-considered duty for the international community to intervene militarily in Ukraine is Russia's nuclear coercion.

In making the first argument—that there is a pro tanto duty to intervene—I will first establish that there is an uncontroversial right to military intervention on the part of the international community. This will establish just cause in assessing whether jus ad bellum applies to members of the international community in joining Ukraine in its fight. My argument will evaluate the other ad bellum criteria for the international community. They are clearly met with respect to military intervention in Ukraine, for at least some members of the international community, with the exception of proportionality, which I will evaluate in the second part of this essay. Then, I will ground the pro tanto moral duty to intervene militarily in a combination of factors, including a right to rescue on the part of Ukrainians; promissory and reliance obligations held by members of the international community; and duties both domestically and internationally related to human rights, security, and international law that cannot be discharged in any other way.

After I have established the pro tanto duty to intervene militarily, I will return to the proportionality calculation, which is decisive for satisfying ad bellum requirements. Because of the high stakes involved for the international community, in addition to the high stakes for Ukrainians, a variety of concerns regarding proportionality in foreign intervention will be dispelled.² I will then focus on the role of Russian nuclear coercion in the proportionality assessment, arguing that it overshadows other considerations in making a proportionality determination. Russia's nuclear coercion could provide a decisive reason not to intervene militarily in Ukraine, especially if noncompliance with Russia's threats would increase the likelihood of limited or total nuclear war more than compliance would. However, I will argue that it is not obvious that succumbing to the threat is the more prudent course of action with respect to nuclear risk. In order to make a concrete determination, we must model the outcomes of a variety of different choices, rather than assuming that the worst-case scenario (localized or total nuclear war) will occur if military intervention is pursued. This is all to say, the question of whether the international community is morally obligated to intervene militarily in Ukraine is the question of whether it is morally permissible to succumb to nuclear coercion; the answer to that question is not at all clear.

Right to Intervene

Russia's aggression in Ukraine and the acts that have accompanied its illegal invasion meet the just cause criterion for jus ad bellum based on two interrelated features of Russia's actions: the mass atrocities and violations of human dignity that characterize Russia's military strategy and conduct, and its illegitimate annexation and rule of the temporarily occupied territories of Donetsk, Luhansk, Kherson, and Zaporizhzhia in September 2022, and of Crimea in March 2014.³ In the remainder of this section, I will discuss the humanitarian components applicable to establishing just cause, which might not be sufficient to provide justification for intervention alone because they typically apply to intervention in the domestic affairs of a country where a government is perpetrating abuses against its citizens, or is unable to stop others from doing so, rather than to interstate conflict.⁴ First, I argue that Russia's illegitimate rule in the temporarily occupied regions of Ukraine confers moral permission for military intervention; that is, that the just cause criterion of the jus ad bellum criteria has been satisfied for the case of a foreign intervention on Ukraine's behalf. For example, David Luban argues that intervention is permissible in cases where a state rules illegitimately, violently, and against the will of the people it governs, even in cases short of slavery or massacres.⁵ Michael Walzer also suggests that intervention is warranted in cases where a “small nation” is “being ground down” in an unequal struggle against a colonizer.⁶ This is certainly the case in Russia's temporarily occupied territories, as discussed later in this section, so it seems there is a case for military intervention on grounds of the illegitimacy of Russia's annexation and rule of large portions of Ukraine. Jeff McMahan refers explicitly to a permission to militarily aid victim states in cases of unjust aggression in general, and specifically in the case of Ukraine (though McMahan thinks Russia's nuclear coercion overrides consideration of direct intervention in the case of Ukraine).⁷ This case is strengthened by humanitarian considerations.

Russia's actions in Ukraine do satisfy the criteria that would justify humanitarian military intervention, even if these criteria typically apply to interventions into domestic affairs. To show this, we can look to Walzer's relatively restrictive account of when intervention in a foreign war is permitted.⁸ On Walzer's account, there are three sets of conditions that can warrant intervention—the third of these, humanitarian intervention, speaks closely to the case of Ukraine. In Just and Unjust Wars, Walzer states that “humanitarian intervention is justified when it is a response (with reasonable expectations of success) to acts ‘that shock the moral conscience of mankind.’”⁹ Walzer's paradigmatic case of such acts is mass slaughter of civilians. Other accounts are more permissive—for example, Fernando Tesón defines permissible humanitarian intervention as “proportionate international use or threat of military force, undertaken in principle by a liberal government or alliance, aimed at ending tyranny or anarchy, welcomed by the victims, and consistent with the doctrine of double effect.”¹⁰ However, we do not need to adopt a more permissive account of humanitarian intervention in order to determine that Russia's actions in Ukraine “shock the moral conscience of mankind.”

Now, I will list some of the many human rights violations, violations of international humanitarian law, and crimes against humanity that have already been documented, and note that efforts to document the scope and extent of these harms are ongoing. As of my writing of this essay in early March 2024, Russia has committed atrocities on a massive scale. Russia has forcibly deported large numbers of Ukrainian civilians, including children (a July 2022 statement by U.S. secretary of state Anthony Blinken estimated that between nine hundred thousand and 1.6 million Ukrainians had been deported by that point in time), to Russia and Belarus.¹¹ It is difficult to estimate the number of forcibly deported Ukrainian children, but estimates range between roughly nineteen thousand and several hundred thousand (Russian authorities claimed that seven hundred thousand children had been “evacuated” by July 2023).¹² Russia has arbitrarily detained, tortured, and summarily executed Ukrainian civilians (90 percent of released detainees interviewed by the UN Human Rights Monitoring Mission in Ukraine for a period covering February 1–July 31, 2023, reported being subjected to torture); the rape and torture of Ukrainian civilians is widespread, reportedly as a specific military strategy; and a July 2023 investigation by the Associated Press provided evidence of sixty-three formal and informal Russian detention facilities in the temporarily occupied territories of Ukraine, with plans to build twenty-five additional prison colonies and six other detention facilities by 2026.¹³ There is no way to know how many people were killed in the city of Mariupol, but early conservative estimates suggested there had been roughly twenty-five thousand civilian deaths (other accounts suggest the number could be over three times that).¹⁴

As occupied territories have been liberated, further evidence of war crimes against civilian populations has been uncovered; including evidence of such crimes in Bucha, Irpin, Izium, Kherson, and elsewhere.¹⁵ An example of the kind of violence Russian forces perpetrate on civilians is described in a report by the United Nations Independent Commission of Inquiry on Ukraine: “In [the] Kyiv region, in March 2022, two Russian soldiers entered a home, raped a 22-year-old woman several times, committed acts of sexual violence on her husband, and forced the couple to have sexual intercourse in their presence. Then, one of the soldiers forced their four-year-old daughter to perform oral sex on him, which is rape.”¹⁶ A number of experts have argued that Russia's actions constitute genocide against Ukrainians, and there has been an alarming amount of rhetoric, both official and officially sanctioned, that expresses intent to eliminate Ukraine as a nation or culture.¹⁷ Any one of the above factors would meet the criteria outlined by Walzer, and I believe that these facts alone justify intervention in Ukraine. Taken together with my earlier discussion regarding the illegitimacy of Russia's rule in the temporarily occupied regions of Ukraine, they overwhelmingly confer a permission to intervene in Ukraine—that is, the just cause criterion for jus ad bellum has been met for military intervention.

Jus ad Bellum

To determine whether nations would be justified in military intervention, we can measure the situation against the remaining jus ad bellum criteria.¹⁸ These criteria are just cause, right intent, right authority, last resort, chance of success, and proportionality.¹⁹ I have discussed how the just cause criterion has already been met. I take it to be evident that intervening to stop atrocity crimes constitutes an action undertaken with the right intent, and that in cases where such crimes are occurring, any member or group of members of the international community has the right authority to intervene.²⁰ A number of authors have argued that humanitarian interventions are rarely just humanitarian interventions—that the reasons for most humanitarian military interventions for humanitarian reasons are in practice coupled with other interests.²¹ The presence of additional, potentially self-interested reasons in cases of humanitarian intervention need not be disqualifying, nor does it weaken the reasons for humanitarian intervention if the reasons for the intervention are sufficiently strong on their own to justify a military intervention. Reasons secondary to humanitarian intervention are acceptable so long as they do not involve unjust aims, such as enrichment at the expense of Ukrainians.²² A just aim would be strong enough both to rationally guide and explain conduct and to satisfy the jus ad bellum criterion of just cause. The other three criteria—last resort, chance of success, and proportionality—require slightly more discussion and will result in different morally relevant considerations. I will leave the discussion of proportionality aside for now, as this will be treated in the final portion of this essay.

A thorough evaluation of whether the international community has met the ad bellum condition of last resort in the case of Ukraine can draw from existing analysis.²³ Different members of the international community have initiated legal proceedings against Russia, applied economic and diplomatic sanctions, and provided military assistance short of direct military intervention.²⁴ The sanctions, legal proceedings, and military assistance to Ukraine have all failed to halt and further prevent Russia's aggression and ongoing abuses. In my view, Russia has made clear that it will not be deterred through nonviolent means; the last resort criterion has been satisfied. However, if there are additional measures that could still be adopted that would substantially increase Ukraine's likelihood of military success without third-party military intervention—for instance, increasing sanctions or providing different weapons—these measures should be pursued. The argument I present will apply in a case where all of the remaining noninterventionary options have been exhausted, which is where I believe we currently find the conflict.

Finally, the criterion of chance of success will limit the extent to which certain specific members of the international community are obligated to assist Ukraine.²⁵ Evaluating the chance of success involves a complex empirical determination that would require evaluating a number of factors. The factors that are relevant to determining the chance of success are also the factors that are relevant to calculating proportionality. These factors will be discussed later in this essay as part of my discussion of proportionality. Crucially, having a high likelihood of success does not require surety of that success, and there are a number of states and entities that would plausibly have a fighting chance against Russia. Determining which members and entities from the international community meet this criterion is also beyond the scope of this essay, but even if no single state met these criteria (which seems unlikely), a coalition of states with the correct makeup would be able to. Therefore, this condition would not pose an obstacle to the satisfaction of the ad bellum criterion in the case of military intervention in Ukraine.

Duty to Intervene

While some scholars have noted that establishing a duty of intervention can be difficult, there are a number of reasons to believe that there is a pro tanto moral duty to intervene on humanitarian grounds, and that the duty bears on the current situation in Ukraine.²⁶ There are several distinct possible grounds for a duty of intervention, including duties that are owed to victims (such as duties of rescue), duties associated with promising (such as through agreements and statements by officials), and reliance duties, as well as obligations owed to the international community more generally and to a nation's own citizens (for instance, with respect to domestic security). Some of these will alone confer a duty to intervene for humanitarian reasons (duties of rescue, reliance duties, obligations owed to the international community), while others will support a duty of humanitarian intervention by providing complementary reasons. In my view, each of these different considerations independently generates strong reasons that support a duty on the part of the international community to intervene militarily to ensure that Ukraine is successful in defeating Russia and securing its territorial integrity; together they provide a strong basis to believe there is a pro tanto moral duty to ensure a Ukrainian victory.²⁷

It is uncontroversial to say that there is a duty of rescue, though the scope of that duty is a matter of considerable disagreement.²⁸ As Simon Caney notes, in order to establish that there is a duty of humanitarian intervention, we must accept that there are certain inalienable human rights, and that those rights generate correlative enforceable duties.²⁹ I will assume a commitment upon the part of the international community to human rights, as evidenced by the adoption of the International Covenant on Civil and Political Rights and other widely adopted documents affirming a commitment to human rights, and I have already provided evidence that Russia has committed gross violations of a number of these rights. These rights generate a duty, grounded in duties of rescue and their corresponding rights, to Ukrainians (and others, including many Russians, who are also having their rights violated by the current Russian regime as a result of the ongoing war of aggression).³⁰ A number of philosophers argue that rights correspond with duties, and I will not defend that position further here.³¹ Suffice it to say, there are human rights and those rights correspond with duties. Because Russia is violating the rights of Ukrainians, and because a large majority of the international community has made a commitment to uphold human rights, there is a right on the part of Ukrainians to have their human rights respected and a corresponding duty to enforce the respect of those rights on the part of the community that has affirmed them.

Promises generate obligations for the promisors to fulfill the content of their promises. In addition to the duties generated by Ukrainians’ right to rescue, there are additional specific duties owed to Ukrainians as a result of various promises made to and agreements made with them. Unlike duties of rescue, which are owed by all members of the international community to Ukraine, promises are only binding on the promisors. A number of nations have made specific promises to Ukraine subsequent to Russia's full-scale invasion, ranging from specific commitments of financial and military support to more general statements regarding support for Ukraine until it achieves territorial integrity. For example, in July 2023, U.S. president Joseph Biden reaffirmed a commitment to help Ukraine, just a few months after a statement of commitment to Ukraine by G7 Leaders in May 2023, which affirmed a commitment to a “just and lasting peace,” and made explicit reference to war crimes and atrocities committed by Russia in its invasion.³² Such statements constitute public statements of commitment. Thomas Scanlon's principle of fidelity supports this view—if I lead you to generate a legitimate expectation that I will act in a particular way, I must fulfill that expectation.³³ This principle covers both statements of commitment and promises, because both of them involve leading a third party to hold a legitimate expectation.³⁴ From a moral perspective, it matters that these statements explicitly commit to supporting Ukraine's territorial integrity, not least because Ukrainian territorial integrity is a necessary condition for the protection of Ukraine's civilian population.

Promissory obligations generated by the 1994 Budapest Memorandum have been discussed at length in a number of venues, but are worth revisiting in a moral context.³⁵ We do not need to determine whether the Budapest Memorandum is legally binding to say that, as a kind of promise by Russia, the United States, and the United Kingdom, it was intended to provide security guarantees to Ukraine, Kazakhstan, and Belarus in exchange for their forfeiture of Soviet nuclear weapons. It is now widely perceived to be a failure.³⁶ This failure signals to nonnuclear states that they should not accept the security guarantees of nuclear armed states, incentivizing proliferation and increasing nuclear risks.³⁷ This failure has also resulted in staggering human costs, borne largely by Ukrainians (as discussed above). It is unambiguous that Russia's repeated incursions on Ukraine's sovereignty violate the Budapest Memorandum (and generate a number of duties for Russia, including to immediately cease hostilities and attempt repair), but the responsibilities of the United States and U.K. in light of Russia's actions have been debated (some have argued that the use of the word “assurance” rather than “guarantee” in the memorandum precludes an obligation to intervene militarily).³⁸ While some relevant issues hinge upon the interpretation of the letter of the agreement, one crucial issue does not—the promisors party to the Budapest Memorandum are morally responsible for its failure and have resulting duties of repair.³⁹ These plausibly, at minimum, include stopping the ongoing humanitarian violations that have resulted from Russia's territorial transgressions.

Besides duties resulting from Ukrainians’ right to rescue, and from the promises made by specific members of the international community, a number of agents have incurred reliance duties by providing Ukrainians with the assistance necessary to keep Russian forces at bay. When I rely on someone, I base my conduct on reasonable expectations that she will act in certain ways.⁴⁰ According to Neil MacCormick, “‘Inducing reliance’ means intentionally or knowingly inducing a person to base his conduct on expectation about one's own.”⁴¹ In aiding and making promises and assurances to Ukraine, a number of different agents have induced Ukraine to rely on them. Critically, when an agent induces reliance, the agent is obligated to discharge the duties incurred by causing the reliance. The obligation is generated because if the agent had not induced reliance, the reliant party could (and likely would) have done otherwise. Any costs the reliant party incurs can thus be attributed to the reliance-inducing agent. This is especially salient in cases where a party has been induced to rely on assistance for survival, or to protect herself from harm. The aid supplied to Ukraine has enabled Ukrainians to protect themselves from Russian attacks, and to continue prosecuting a war against Russia; the provision of aid, coupled with promises of aid for “as long as it takes,”⁴² has induced Ukrainians to conduct themselves in a way that they might not have otherwise. Providing this aid with the intention of fueling a Ukrainian military victory generates moral obligations to assist in that victory. Ukraine likely would not have been able to defend itself without this aid; this is precisely why enabling Ukrainians to survive generates duties for those who have helped the country. By sending aid in the first place, other countries induced Ukraine to rely on them, because coupled with statements of ongoing support, Ukrainians should have been able to reasonably expect continued assistance.

My argument so far has been that there are pro tanto moral duties, based in principles of rescue, promises, and reliance, to Ukrainians. All things considered, there may or may not be considerations that outweigh these duties—this is one of the open questions this essay seeks to highlight. One might concede that there are humanitarian duties to Ukrainians as a result of Russia's war of aggression but still raise one of two worries—that those duties are outweighed by either the costs of aiding or by stronger duties to the populations of the nations that would be aiding Ukraine. The first worry, that the costs outweigh the strength of the claims, will be discussed at greater length in the next section of this essay, and it will be weakened by the discussion of the second worry that follows.

The concern that duties to citizens of one's own nation may outweigh duties to Ukrainians is unfounded. Such an argument might say that a nation ought to attend to the needs of its own citizens before attending to the needs of others. However, this rests upon an assumption that the outcome of the war in Ukraine and the means by which it is fought are irrelevant to the concerns of citizens of countries other than Ukraine.⁴³ This is false. Even if we think that governments have specific duties to their own citizens that supersede the duties they have to citizens of other countries in cases where the two conflict, this is not a case in which they conflict. Because of international prohibitions on wars of aggression and because of international norms upholding human rights, the outcome of the war is salient to the entire international community. A Russian victory also poses a distinct security threat to a number of specific nations.

One may raise the objection that, faced with limited resources, a government must weigh providing aid to a foreign country against providing domestic goods. This may be true as a general claim; however, depending on the particular circumstances, it may not be a simple question of whether to help other nations or your own. Depending on the domestic security risks posed by a failure to aid, the question may become one of how to best help your own nation; for example, the choice may be between providing particular goods and ensuring the nation is not under attack. The security threat posed by a Russian victory is critical to the domestic security of a number of nations, to varying extents, both because of the nuclear dimension, which will be discussed below, and because of the conventional military threat a Russian victory would pose to specific nations, including NATO members. These considerations are evident in the reasoning articulated by Poland and the Baltic countries for their staunch support of Ukraine. Russia poses significant security risks to the United States as well. Not only does Russia describe itself as being at war against the “collective west” but it has also engaged in election interference, disinformation campaigns, and the unlawful detention of American citizens, including the journalist Evan Gershkovich.⁴⁴ This conduct interferes with the United States’ most basic institutions—fair systems of governance and freedom of information—posing a direct threat to U.S. democracy. The nature of the threat Russia poses to different nations is context specific, but these examples illustrate the ways in which the war in Ukraine should be viewed as a critical domestic issue for quite a few countries.

There is also a broader duty to the international community generated by setting precedents that erode the legitimacy of international law and global security, as well as in the UN Charter, which generates promissory obligations. In acting as bystanders to atrocities and the gross disregard for international law, members of the international community become complicit in these crimes, plausibly including genocide, and, in doing so, ensure that the entire world is worse off, which has a direct impact on their own citizens.⁴⁵

One may object to the statement that the international community is acting as a bystander to atrocities and reference the military aid, legal proceedings, and sanctions that are being provided by a number of international actors. However, these have been ineffective so far, and will likely be insufficient to ensure a Ukrainian victory. Also, the fundamental consideration underpinning this assistance is that it will result in a Ukrainian victory. It would be unjust to support a war unless that support were offered with the objective of military victory as its goal. It is immoral to provide insufficient assistance because it condemns Ukrainians to a slower, but still almost certain, demise. This is akin to putting someone in a leaky lifeboat that will not get them to safety. Provision of insufficient aid is especially unjust not only because it condemns Ukraine but also because of the bearing of the war on the security of the international community since a Ukrainian loss would make everyone worse off. It is because so many countries are assisting Ukraine with military assistance short of direct intervention that it is incumbent upon them to fully commit to the objective—a Ukrainian military victory—that their ongoing assistance implies.

Proportionality and Nuclear Escalation

So far, I have argued that there is a right for certain members of the international community to intervene militarily in Ukraine, and I have argued that for several of them, there is also a pro tanto duty to intervene militarily in Ukraine. In order to establish jus ad bellum for humanitarian military intervention in Ukraine, I have evaluated the case for military intervention against all of them, save proportionality. Jus ad bellum proportionality considers the harms a war inflicts against those it prevents.⁴⁶ I have given a limited picture of the kinds of harms Russia is inflicting both against Ukrainians and against the laws, norms, and moral standing of the international community (as well as against Russian citizens). These harms are grave, and I have argued that they generate obligations for military intervention on the part of certain members of the international community.

How should we measure the costs then? There are a number of ways to consider this question—we can examine the harms, on one side, and the costs, on the other, wholly as a matter of numbers of lives lost, destroyed, or saved, with no regard to nationality, stake, or justice of cause, or we can consider whether to weigh certain costs more heavily (for instance, those borne by Ukrainian civilians). We can also consider whether some parties to the conflict bear a greater liability to be killed, such as Russian soldiers, and partially discount their deaths when calculating costs.⁴⁷ We may ask the question of whether the intervening force would bear undue costs as a result of the intervention.⁴⁸ Accepting that members of the international community have a direct stake in the outcome of the war entails that they are liable to bear some significant cost; the cost they are liable to assume results directly from the risks a Russian victory poses both to the international community as a whole, especially with respect to a rules-based international order that affirms human rights, and to the citizens of a number of individual countries in particular. Thus, I will leave aside considerations of claims that there are no justifiable costs that the international community should bear. A proper proportionality calculation, then, will involve calculating the harms that would result from military intervention and from nonintervention. Calculating this cost will be highly sensitive to the mode and means of intervention. Because I have argued that certain members of the international community have a duty to ensure Ukraine's victory, we should consider the least harmful means that would enable this outcome. If this duty is accepted and Russia were not a nuclear power, this calculation would involve projections of losses in a conventional war, and it would almost certainly come out in favor of a coalition of states that came to Ukraine's aid. Russia is, however, a nuclear power, and, further, Russia has taken an increasingly hostile nuclear stance. In addition to generalized statements that a defeat of Russia in Ukraine could trigger a nuclear war, Russian president Vladimir Putin has specifically stated that Moscow is prepared to use nuclear weapons if its “territorial integrity” is threatened, with reference to the territories in Ukraine that Russia is illegally occupying.⁴⁹

However, driving Russian forces out of Russia's temporarily occupied territories in Ukraine is precisely what is morally required. Because Russia has threatened a nuclear response to this outcome, the relevant proportionality calculation involves measuring the harms involved in nonintervention, which have been described above, against the harms involved in intervention, which, because Russia has threatened to use nuclear weapons, involves assessing Russia's nuclear threat. One must then model different possible outcomes and their likelihoods of obtaining. The most morally relevant feature of the proportionality calculation for the relevant parties is the costs these parties are likely to bear as a result of intervention with respect to nuclear weapons use. This is because other features of the proportionality calculation—namely, casualties resulting from a conventional war—would be unlikely to tip the balance against intervention (though the costs of a conventional war are not irrelevant to this consideration either, especially because wars are difficult to end once they have started and because casualties mount as they proceed).⁵⁰ That is, the question of whether to intervene in Ukraine can be reduced to the question of whether it is permissible to succumb to Russia's nuclear coercion.

A common mistake at this stage is to end the evaluation here. The mistake proceeds as follows: because Russia has threatened the use of nuclear weapons, we should assume that it will act on its threats, and, further, that its doing so (thus breaking the nuclear taboo) would lead to total nuclear annihilation.⁵¹ This argument assumes the worst-possible outcome at each stage of evaluation and proceeds as if each of those worst-possible outcomes would actually obtain, rather than treating the worst-possible outcome as one of many that are possible. A proponent of this argument might respond to this critique by pointing out that while the worst-case scenario is one of several possible outcomes, because there is a nonzero chance of that worst case obtaining, the risk involved in selecting a choice option (military intervention in Ukraine) that would elevate that risk to any degree is automatically morally impermissible, and therefore military intervention in Ukraine is morally impermissible. This might be compelling if it were certain that the risk of nuclear weapons use would be lower in the case of nonintervention. However, I will now argue that it is far from obvious that the risk of nuclear weapons use is lower in such a case. This is one of the primary reasons why it is a mistake to assume that succumbing to nuclear coercion in this instance is morally justified. This requires some unpacking.

Succumbing to nuclear coercion may not prevent risks of nuclear weapons use from rising. Suppose the threshold of nuclear risk prior to Russia's full-scale invasion of Ukraine is at some specific nonzero level, and when Russia threatened to use nuclear weapons in Ukraine in a range of scenarios, the threshold increased by some amount; that increase will likely be determined by a variety of different variables, including types of actions more or less likely to lead Russia to use nuclear weapons; how well or poorly Russia's aims in Ukraine are being satisfied; the extent to which Russia expects a favorable outcome in the war; the viewpoints of Russian allies (such as China); and other factors.⁵² Suppose that a military response by allies of Ukraine has an effect on some of these variables, such that the increase in risk rises or falls based on those actions. For example, hypothetically, imposing a no-fly zone coupled with a weak threat of conventional retaliation for the deployment of tactical nuclear weapons might increase the risk level, while provision of strong conventional assistance to Ukraine coupled with responsive nuclear coercion might decrease the risk level.

Doing nothing also has an impact on the level of nuclear risk.⁵³ It is not difficult to imagine a case in which no external parties intervene militarily in Ukraine, and Ukraine is, after incurring staggering military losses and suffering even more human rights abuses than have already occurred, forced into a territorial negotiation with Russia, conceding the currently temporarily occupied territories. Russia may take the lesson that nuclear coercion is an effective strategy in the global arena, and may be emboldened to continue its expansionary objectives. Indeed, this should be taken seriously, as Russian officials have made statements indicating that potential future targets could include Poland, the Baltics, Kazakhstan, and others.⁵⁴ This could lead to continued and escalated nuclear threats in future military actions, and these threats have the potential to be deadlier if possible targets include NATO member states that have treaty obligations to defend one another; a Russian attack on a NATO member would almost certainly trigger an escalation in hostilities. We can also look to Russia's past behavior in Georgia in 2008 and Crimea in 2014 for evidence both that Russia's aggressive posture is unlikely to be curbed by compliance and that its threats are likely to continue escalating.⁵⁵

The messaging that other belligerent or potentially belligerent states take from Russia's war of aggression is also extremely salient to our moral reasoning. We should think that any credible nuclear threat genuinely does increase the level of nuclear risk. Empty nuclear threats are ineffective, so we should assume that no nuclear threat is completely empty. Even if the risks are low in each instance, someone who is risk averse with respect to nuclear weapons should want to minimize them. If Russian nuclear coercion continues to successfully deter potential allies of Ukraine from coming to its assistance, other nations will learn from this, and we should expect to see an increase in nuclear threats made. Chinese military analysts have already noted the apparent success of Russian nuclear coercion, which could provide a grounding for expansion of the Chinese nuclear arsenal.⁵⁶ Allowing Russia's aggression to succeed in Ukraine will set an extremely dangerous precedent for future nuclear coercion by both Russia and other nuclear armed states and corresponding increases in actual nuclear risks, not to mention other moral risks such a precedent would incur.⁵⁷

These hypothetical considerations are not meant to show conclusively that there is any particular increase or decrease in nuclear risk associated with any particular action or inaction—what I mean to show is that it is not at all obvious that declining to intervene militarily in Ukraine actually lowers the threshold of nuclear risk that we have already reached, and that these considerations must be taken into account. There is a massive literature on nuclear risk and strategy, reference to which would be required to draw any definitive empirical conclusions.⁵⁸ However, there are reasons to believe that my account warrants serious consideration. A recent National Academy of Sciences, Engineering, and Medicine consensus study report produced research that was intended to reflect the current scientific consensus of the best methods of analysis for assessing risks of nuclear war and nuclear terrorism.⁵⁹ This report notes that four main risks emerge from the literature on risk assessments related to nuclear deterrence: “the reciprocal fear of surprise attack, the threat that leaves something to chance, the commitment trap, and the risk of inaction” (emphasis my own).⁶⁰ In this essay, I have suggested that it is a mistake to ignore the risk of inaction in making assessments about total nuclear risk; this claim is supported by the report, which says that this risk “is poorly understood in much writing about deterrence,” and that “not taking action certainly entails risks.”⁶¹ Here, I have been suggesting that this risk needs to be explored fully in order to draw conclusions about what course of action allied nations should pursue in Ukraine.

The real risks of all possible courses of action should be outlined and considered, including those resulting from succumbing to Russian nuclear coercion. The existing proliferation of nuclear weapons already raises the threshold above zero. So rather than ending the conversation with a nod to increased nuclear risks, we ought to consider what those risks actually are, and whether they are actually or unacceptably higher than the nuclear risks we already live with, the moral risks we incur by nonintervention in Ukraine, and the nuclear risks involved in nonintervention. The answer may be that the risks of intervention are in fact too high, but we cannot assume that without considering the range of possible outcomes, including the actual likelihood of nuclear weapons use by Russia, and the potential effectiveness of conventional intervention coupled with nuclear deterrence strategies on the part of nuclear armed allies (for example, stating that any first strike by Russia would be met with either a strong conventional response against Russia or a nuclear response against Russia). This all suggests that the problem is very difficult, and there is likely to be disagreement, even among reasonable agents with similar moral values. Determinations of how to weigh each morally relevant factor in such an equation will depend on making judgment calls on a number of moral issues that are far from settled within moral philosophy.⁶² We might think that it is impossible to make such a decision with the confidence that we have acted rightly.

The analysis of each possible scenario is outside the scope of this essay, but this analysis would be required to determine what sorts of responses are appropriate. Sanctions are not working; it is increasingly clear that a victory by the Ukrainian military alone is elusive; and it is incumbent upon the international community to assist Ukraine in achieving victory. It is also incumbent upon the international community to minimize the risks of a nuclear war. A nuclear risk–averse account of the duties of the international community might prescribe better and swifter deployment of additional military aid, and it might consider targeted killings of Russian officials. This account will have to take seriously the fact that the actions taken by Ukrainian allies have been unsuccessful in stopping Russian aggression and its steep moral costs, without necessarily having diminished the risk of nuclear war.

Conclusion

None of my arguments here should be construed to prescribe a particular course of action. What I have intended to show is that one of the most morally salient questions related to the war in Ukraine is whether the international community should intervene militarily, and that the most relevant consideration with regard to this question is the impact intervention or nonintervention would have on the risk of nuclear war, either in this case or in the future. It may seem, as many assume, that the nuclear risks associated with intervention are too costly to bear, no matter the other stakes. However, this assumption is too hasty. Succumbing to Russian nuclear coercion in the face of massive human rights violations would set a dangerous precedent, which would be noted by hostile would-be aggressor states. If nuclear coercion is successful in deterring a justified and, as I have argued, pro tanto obligatory military intervention today, then we should expect to see future instances of nuclear coercion accompanying violations of territorial integrity and abuses of human rights. Because each threat, even if it has a low level of credibility, lowers the threshold for nuclear weapons use, a future in which we can reasonably expect repeated nuclear threats is one in which nuclear risks are heightened. On the other hand, a rupture of the nuclear taboo in this instance would also lower the threshold for future nuclear weapons use, so any actions taken on the part of the international community would need to have a high chance of success coupled with a high degree of confidence in their own ability to deter Russia from using nuclear weapons. The fact of the matter is that this is a complicated equation, whose balance is highly dependent on a number of volatile factors, and any action or nonaction carries both nuclear and moral risks. The moral stakes are also very high—insufficient action sets a dangerous precedent with respect to nuclear coercion, erodes norms related to human rights and international law, and condemns Russia's victims to unimaginable suffering.