The end of the First World War was a crucial time for nationalist leaders and minority communities across the European continent and beyond. The impact of the post-war spread of self-determination on the redrawing of Eastern European borders and on the claims of colonial independence movements has been extensively researched. By contrast, the international historiography has paid little attention to minority nationalist movements in Western Europe. This article focuses on three regions (Catalonia, Flanders and South Tyrol) that experienced considerable substate national mobilization in the interwar period. The article aims to understand whether the leaders of Western European minorities and stateless nations shared the same enthusiasm as their anti-colonial and Eastern European counterparts for the new international order that self-determination seemed to foreshadow in the months following the end of the Great War. Because President Woodrow Wilson stood out as the most prominent purveyor of the new international legitimacy of self-determination, the article further examines how Western European nationalist movements exploited Wilson’s image and advocacy to achieve their own goals. Nationalist forces in Catalonia, Flanders and South Tyrol initially mobilized self-determination and referred to Wilson as a symbol of national liberation, but this instrumentalization of self-determination was not sustained. Large-scale mobilization occurred only in Catalonia and, even there, it disappeared almost overnight in spring 1919. Furthermore, substate nationalist movements in Western Europe tended to mobilize self-determination to gain regional autonomy, rather than full independence, thus pursuing internal, not external, self-determination. The willingness of these movements to privilege autonomy over full independence made them more receptive to compromise. Radical forces would become stronger only in the 1930s and largely for reasons not directly connected to the post-war mobilization around self-determination.