The ban on inter-state war in the UN Charter is widely identified as central to the modern international order-Michael Byers calls it 'one of the twentieth century's greatest achievements'. Even if it is only imperfectly observed, it is often seen as a constraint on state autonomy and an improvement on the pre-legal, unregulated world before 1945. In response to this conventional view, this article shows that the laws on war in the Charter are better seen as permissive rather than constraining. I make two points. First, by creating a legal category around 'self-defence', the laws on war authorise, and thus legitimate, wars that are motivated by the security needs of the state, while forbidding other motives for wars. Second, state practice since 1945 has expanded the scope of this authorisation, extending it in both time and space beyond the black-letter text of the Charter. The permissive effect of law on war has therefore been getting larger. These two effects suggest that international law is a resource that increases state power, at least for powerful states, and this relation between international law and power politics is missed by both realists and liberal internationalists.
KeywordsSelf-defence; International Law; International Security; Laws of War; Legal Justification He who breaks the law has gone to war with the community; the community goes to war with him. 1In the standard view of international law, the power of law lies in its ability to differentiate between lawful and unlawful state behaviour and to encourage the former by making the latter more expensive. However this model fails in relation to the laws that ban inter-state war, and it fails for reasons that are important for scholarship on the relation between international law and politics. This article makes two points: that the laws on war are permissive rather than constraining and that the scope of this permission has expanded since 1945 under the influence of state practice. Contrary to the conventional view of the ban on war, raisons d'état are not supplanted by legalism. Legalisation has instead created a legalised path for war through the concept of self-defence. This amounts to a permissive authorisation for war that magnifies some aspects of state power, with a scope that has been expanding since 1945.The ban of war is widely identified as central to the modern international order -Michael Byers calls it 'one of the twentieth century's greatest achievements' -and it is often used as evidence of progress