In debates about the role of federalism in America, much turns on the differences between states. But what about divisions within states? The site of political conflict in America is shifting: battles once marked by interstate conflict at the national level are increasingly reflected in intrastate clashes at the local. This shift has not undermined the role of federalism in American politics, as many predicted. Rather, federalism's role has evolved to encompass the growing divide within states and between localities. In other words, federalism disputes — formally structured as between the federal government and the states — are increasingly being used to negotiate intrastate conflicts. This article describes how and why this transformation has taken place. Foregrounding this development shines light on the local roots of many of the most sensational federalism disputes in recent years — from immigration to drug policy. It also explains why, contrary to traditional models, federalism battles frequently involve states that are fiercely divided and undergoing political change.