The project is devoted to the international relations in East-Central Europe between the wars (1919—1939). Twenty years of peace produced many visions of the reconstruction of the international order in this region (e.g. Little Entente, the project of the Danubian Pact, the Polish idea of the Intermarium Block, the German Mitteleuropa). Two opposite ideas of foreign policy dominated the international politics of post-war Europe: “liberal internationalism” and “exclusivist nationalism”. Was an East-Central European Federation only an illusion? This is the question approached in historiography but the initiatives leading to an integration of East-Central Europe after World War I, divided into national states, requires a new study.