This chapter introduces the debates regarding the development of jus ad bellum, with a particular focus on the development of the definition of force and the right to self-defence. It discusses the relationship between the rules of the UN Charter and customary international law, and the way in which development of custom, as well as debates amongst other international actors, contribute to the dynamic interpretation of the Charter rules.

This concluding chapter argues that conventional approaches addressing the development of customary international law relating to the use of force are unable to make sense of the changing practices and technologies that are explored throughout the book. It is argued that rather than focusing on an ambiguously defined requirement of publicity, practice will meet the minimum qualitative requirement as soon as it is publicly known and acknowledged. The chapter further highlights how methodological choices relating to the positioning within international lawmaking of covert operations that are publicly known contribute to the creation of spaces for a range of actors seeking to influence the development of the law. By positioning some acts as ‘outside’ of the international lawmaking process, it leaves open new opportunities to decide what the acts are, and how they should be responded to.

This chapter examines quasi-covert conduct, that is, acts that are acknowledged and justified in part; hypothetical justifications not related to an acknowledgement of actual conduct; and acts that are acknowledged or justified after some time. Focusing primarily on the United States’ drone strikes in Pakistan under the Obama administration, it is demonstrated how quasi-covert operations pose significant challenges to the development of international law by creating uncertainty as to the way in which specific conduct may alter international law, and as to when states need to react in order to avoid their silence being interpreted as acquiescence.

This chapter focuses on the development of customary international law and unpacks the requirement of publicity for state practice. It introduces the different levels of publicity and covertness, and closely examines the role of acknowledgement, justifications, and public knowledge within the requirement of publicity in the light of various approaches to the development of (customary) international law. The chapter illustrates how the requirement of publicity can be unpacked into two main parts, where the first relates to how a state communicates its understanding of its practice in relation to international law, and the second relates to how the act itself and — if available — the justifications provided for it, are known and reacted to by other states and international actors.

This chapter demonstrates how covert operations differ significantly in their level of publicity, and range from acts that remain secret, to acts that are the object of debates amongst states, legal scholars, and civil society, in and outside the settings of international organisations. It is demonstrated that unacknowledged acts can affect the law in different ways depending on their level of publicity and covertness. It will also be shown that the necessity of the involvement of states in a debate around an operation can vary depending on the rule that it is informing. An unacknowledged act leading to extensive academic debate might prove very informative and play an important role in updating the already vague definition of ‘force’ in light of technological developments, but it would not have the same effect if arguing for a right to preventive self-defence against non-imminent threats, where states have been more active in the debate. It is further argued that the absence of states from certain events and debates opens up more influential participation by other international actors, such as legal scholars and other groups of experts.

This introductory chapter intsroduces the themes, context, and structures of the book.