The chapter addresses the use of force against terrorists abroad. The use of force against non-state actors may be authorized by the UN Security Council. More controversial is the use of force against terrorists in self-defence. Reliance is sometimes placed on the ‘unable and unwilling test’ and on ‘anticipatory self-defence’; neither is (yet) accepted by states generally. It is submitted that the existing rules of international law on the use of force are adequate (and anyway are not going to change anytime soon). What is needed is a greater degree of common understanding among states as to the application of the jus ad bellum in the face of modern terrorist threats.
Omri Sender and Michael Wood
The present contribution seeks to provide a general overview of the theory and practice concerning the question of how customary international law emerges. Raising some of the central issues rather than offering hard-and-fast answers, it suggests that although the process of formation of customary international law may defy exact definition in light of its inherently informal nature, important signposts exist for those who seek them. In particular, while scholars continue to debate how customary international law is generated, a shared understanding of the essential requirements does exist in practice among States and various international actors, who continue to regard customary international law as deriving from ‘a general practice accepted as law’. Such an understanding of how customary international law comes into existence and what it essentially is, is crucial for establishing a greater certainty with regard to its content and for the legitimacy of international law more broadly.