This chapter looks at the First World War, which would decisively shape democracy’s rise in international politics. When the war commenced, it was fought for old-fashioned reasons, with little concern for democracy. This changed drastically in 1917, due to revolution in Russia and America’s entry into the war. The reframing of the conflict as one of democracy versus autocracy was facilitated by events in Russia, but it was Woodrow Wilson’s intervention that was crucial in thrusting democracy onto the international agenda. With the defeat of the Central Powers, popular sovereignty supplanted monarchy as the dominant form of state legitimacy. This also confirmed democracy’s remarkable ideational transformation into a normatively acceptable, and for many desirable, method of government. The final section of the chapter considers the attempts to build a new international order at Versailles and the role that democracy played in these plans.