In thinking about the twentieth century, 1945 marks an obvious – in some ways perhaps too obvious – caesura. Certainly much changed after the Second World War, if not always as much as at first it seemed. Among the many apparent changes, one of the most striking was the transformation in the relationship between law, especially international law, and mass violence. For a time, it seemed as if a new era had dawned in international relations, one in which law and international institutions would supplant force and the nation-state as the key determinants of world order. For the optimists, and there were no small number of these in the late 1940s, the catastrophe of the Second World War seemed to have fundamentally altered the global equation, creating an opportunity, even a necessity, for a fundamental transformation in the way global politics worked.

Reason, not power, law, not violence, would henceforth govern world affairs. Organized mass violence, if not abolished outright, would be subject to strict legal regulation. Aggressive wars would be prevented or stopped by united world action operating under the rule of law. Mass atrocities would be dissuaded and penalized by international criminal law. In general, the expectation was that the new United Nations would create an international order that sharply limited global violence and that codified and protected what were coming to be called human rights, even if this meant intervening in the domestic affairs of member states. Although the UN was in many ways simply intended to be a more efficient version of the League of Nations, the new legalism of the post-1945 period was meant to be far more comprehensive than its predecessors. It was intended, as A. H. Feller, General Legal Counsel for the UN, declared in 1949, to mark a gradual move “toward world law.” “The trouble with international law is not that it isn’t law,” Feller maintained,

The legalist paradigm that emerged after World War II thus strove to recapitulate on an international scale the domestication of mass violence that had occurred within the nation-state in the Early Modern period.