In the late nineteenth century the United States oversaw a great increase in extraterritorial claims, boundary disputes, extradition controversies, and transborder abduction and interdiction. In this sweeping history of the underpinnings of American empire, Daniel S. Margolies offers a new frame of analysis for historians to understand how novel assertions of legal spatiality and extraterritoriality were deployed in U.S. foreign relations during an era of increased national ambitions and global connectedness. Whether it was in the Mexican borderlands or in other hot spots around the globe, Margolies shows that American policy responded to disputes over jurisdiction by defining the space of law on the basis of a strident unilateralism. Especially significant and contested were extradition regimes and the exceptions carved within them. Extradition of fugitives reflected critical questions of sovereignty and the role of the state in foreign affairs during the run-up to overseas empire in 1898. Using extradition as a critical lens, Spaces of Law in American Foreign Relations examines the rich embeddedness of questions of sovereignty, territoriality, legal spatiality, and citizenship and shows that U.S. hegemonic power was constructed in significant part in the spaces of law, not simply through war or trade.