The idea of bringing into being supranational organizations to resolve disputes between states has a distinguished lineage, going as far back as Dante Alighieri’s On World Government, Rousseau’s A Project of Perpetual Peace and Kant’s proposal for a federation of nations operating under the rule of law, and eventually evolving into “a perfect civil union of mankind.” The League of Nations was a first attempt to pool national sovereignties together to deal with the problem of war, a milestone in a long process intended to strengthen the effectiveness of mechanisms of international cooperation. The UN was initially conceived as an international entity founded on federalist principles, with substantial powers to enact laws that would be binding on member states, but it emerged as a rather less ambitious entity with two fundamental flaws: the principle of one country–one vote in the General Assembly and the veto within the Security Council, both undermining the democratic legitimacy of the organization. The chapter also reviews the concerns raised by Grenville Clark and others who thought that if member countries could not agree upon well-defined powers that they would be willing to yield, no global authority adequate to maintain peace would arise in our time.