A rediscovery of the long-forgotten republican version of liberal political theory has arresting implications for the theory and practice of international relations. Republican liberalism has a theory of security that is superior to realism, because it addresses not only threats of war from other states but also the threat of despotism at home. In this view, a Hobson's choice between anarchy and hierarchy is not necessary, because an intermediary structure, here dubbed "negarchy," is also available. The American Union from 1787 until 1861 is a historical example. This Philadelphian system was not a real state since, for example, the union did not enjoy a monopoly of legitimate violence. Yet neither was it a state system, since the American states lacked sufficient autonomy. While it shared some features with the Westphalian system such as balance of power, it differed fundamentally. Its origins owed something to particular conditions of time and place, and the American Civil War ended this system. Yet close analysis indicates that it may have surprising relevance for the future of contemporary issues such as the European Union and nuclear governance.