Recent scholarship discussing the ‘federal moment’ in world history after 1945 has re-examined alternatives to the nation-state in the years of decolonization, arguing against any inevitable transition from empire to nation. This article focuses on the case of East Africa, where federation seemed an attractive and likely prospect by 1963, yet never came to pass. Here, the politics of federation should be understood as a constitutive part of the contested nation-state-making process, rather than a viable alternative to it. For the leaders who initiated the politics of federation in the 1960s, regional unity promised the further centralization of power and a means of defeating ‘tribalist’ opposition. For their opponents, federation was seized on as a means of promoting the autonomy of provinces or kingdoms within a larger federal unit. Ultimately, regionalist aspiration was inseparable from national politics, and negotiations among the leaders of East African states demanded the definition of national interests which divided states rather than united them. Such conclusions suggest that historians of the federal moment might more productively focus on the functions of federalist discourse in the making of nation-states rather than debating the viability of federalist projects.