The study explores the possibility of an equitable further development of the so-called Kantian Project: In which direction evolves international law since the propagated »End of the Westphalian System«? How will the Kantian project further be completed, in view of the simultaneity of a constitutionalization process in international as well as transnational law and an enormous military asymmetry? Despite the emerging BRICS-countries the defense budget of the US is as large as the next ten states added together. The simultaneity of constitutionalisation and unipolarity involves certain risks. Great powers can instrumentalize international institutions for their own purposes and impose their will on other states. This undermines the legitimacy of the overall order. If the constitutionalisation process should be truly global, the debate and the question of the legitimacy of European Universalism must be added to the question of the legitimacy of Global Governance. Therefore the article deals with a twofold legitimacy problem. Amazingly, in Greek antiquity there was a regional forerunner of our modern global peace order: the so-called Koine Eirene contracts. These multilateral peace contracts established a system of collective security to end the Peloponnesian war (431–404 BC, fought between Athens and Sparta with their respective allies). Immanuel Kant took those multilateral peace agreements as a model for his »Perpetual Peace« and the »League of Nations«. Even in the ancient model the order had to be supported by a hegemon (Macedonia), who exploited his position – as well as the US hegemony today. What are the lessons from history?