This article offers a gender re-reading of the international history of the post-First World War peace process, a period when nationalism is said to have reached its ‘apogee’, when national self-determination and mutual cooperation between nations in the form of a League of Nations defined liberal aspirations for a democratic new world order. It was also a period when international women's organisations emphasised female self-determination as both a national and international issue. Juxtaposed, these two aspects of the history of the peace of 1919 shed light on the importance of sex difference to the idea of national self-determination and to the overlapping constitution of the national and the international as spheres of political agency and influence in the early twentieth century.