World War I revealed a German imperialist project of eastern expansion, whose dizzying success and equally sudden failure lastingly destabilized international politics. Resulting patterns of nationalist grievance and assertiveness, matching greater-national revanchism to national-minority predicaments, proved impossible to manage or contain. In registering the collapse of the prewar multinational empires (Germany, Austria-Hungary, Russia, Ottoman Turkey), the Treaty of Versailles and its supplements redistributed territorial-political sovereignty among freshly constituted republican nation-states (“successor states”), in an international system to be guaranteed by the League of Nations. Launched by Lenin and coopted by Woodrow Wilson, the discourse of “national self-determination” only imperfectly described this European state-making conjuncture. At the same time, it inspired newly emergent anti-colonial nationalisms in the extra-European imperial world. Each effect seeded problems for the future.