This chapter analyses how an international wrongful act accrues from the violation of a due diligence obligation and its consequences. The first part discusses due diligence obligations against secondary rules of ARSIWA concerning the existence of a wrongful act. It is argued that violations of due diligence obligations stem from omissions and that the difficulty of establishing responsibility for failure of due diligence typically concerns the application of rules governing the breach, rather than rules of attribution of conduct. Accordingly, a critical reappraisal of the genealogy of Article 14(3) of ARSIWA and breaches of preventive obligations is undertaken; the chapter argues that the ILC wrongly conceptualised the ‘event’ to be prevented as a secondary rule, this way confusing the relationship between prevention and due diligence. The rest of the chapter examines due diligence obligations against other relevant secondary rules, such as circumstances precluding wrongfulness (specifically, force majeure and distress), the relationship between due diligence and complicity, and how reparation is to be accorded following a breach of due diligence obligations.

Due diligence has increasingly attracted the attention of scholars but it remains an elusive concept. This chapter explains why a study on the dogmatic foundations of due diligence obligations is timely. Thechapter argues that studies addressing the theory of public international law obligations are still scarce. Yet, they are crucial for properly understanding the externalities of obligations and their functioning on the international legal order. Starting with this premise, the chapter asserts that a theoretical study on due diligence obligations serves two main purposes. First, it allows to better clarify the nature, the content and the scope of operation of these obligations, which are traditionally considered difficult to pin down in the abstract. Second, the chapter advances the hypothesis, to be tested in the course of the book, that a dogmatic reconstruction of due diligence obligations also serves normative purposes. The introduction then sets the methodology and scope of the book and explains why the study of due diligence obligations will be limited to obligations of states and will not cover due diligence obligations of international organisations and non-state actors.

This chapter explores the foundations of due diligence under international law. Due diligence emerged in the international practice of the nineteenth century concerning diplomatic protection and the security of states, and developed as a notion linked to the responsibility of states in connection with acts of private individuals. For a long time, due diligence was conceived as a concept pertaining to the realm of international responsibility and it was primarily associated with the measure of a state organ’s fault. The chapter illustrates how, during the twentieth century, due diligence migrated from the realm of secondary rules to primary rules. The chapter clarifies the relationship between due diligence and overlapping concepts, like international liability and the notion of general principles of international law. It is argued that due diligence should be construed as an identifier for a typology of international obligations, something that provides meaning and rationale to them. The chapter concludes by clarifying the difference between due diligence as a ‘qualifier’ for primary rules of states, and due diligence as a ‘process’ linked to the activities of non-state actors.

A basic framework for classifying institutions and thinking about their role in economic development is illustrated with the colonial experience of the British and Spanish empires in the eighteenth and nineteenth centuries, and Japan in the nineteenth century. Institutions are the ‘rules of the game’. Primary rules are rules that apply directly to individuals and their relationships. Secondary rules are the ‘rules for making the rules’. The secondary rules governing the Spanish Empire located the procedures for making new rules and changing existing rules in negotiations with the king. Secondary rules in the British Empire located many of the processes for making new rules in the colonies themselves. Faced with independence and the end of monarchical rule in the late eighteenth and early ninteenth century, the institutions in the former Spanish colonies had to be reinvented from whole cloth, as the basic structure of secondary rules was no longer viable. In the British North American colonies, secondary rules allocating authority to colonial legislatures remained in place and were gradually transformed after independence. Japan, in contrast, wrestled with how to structure secondary rules in the events leading up to and following the Meiji Restoration.

Chapter 9 delves into juridical military necessity as an exception. It begins by distinguishing juridical military necessity from the state of necessity, a circumstance precluding the wrongfulness of an act under the international law of state responsibility, on account of their distinct normative status and distinct contents. The discussion then proceeds to the four cumulative requirements customary IHL imposes when invoking express military necessity clauses. First, the measure must be taken as primary for some specific military purpose. Second, the measure must be ‘required’ for the purpose’s attainment. This requirement may be sub-divided into three components, namely relevance, minimum injury and proportionality. Third, the purpose must itself conform to IHL. Fourth, the measure must also conform to IHL.