This article traces the evolution of the political meaning of secession from an action taken by a state within a compact or union, to an action available to a nation within a state. It is argued that this evolution, often forgotten in the customary attention given to national self-determination in international law and international relations theory, is associated not only with the modern emergence of nations and of states, but also with the emerging importance of the United States in international affairs at the turn of the twentieth century. The article puts the phenomenon of secession, currently dominated by attention to the Balkans, in a broader context by examining features of four cases: the American South, the Irish Free State, Bangladesh and Quebec.