This study provides the first book-length account of U.S.-Habsburg relations from their origins in the early nineteenth century through the aftermath of World War I and the Paris Peace Conference. By including not only high-level diplomacy but also an analysis of diplomats' ceremonial and social activities, as well as an exploration of consular efforts to determine the citizenship status of thousands of individuals who migrated between the two countries, Nicole M. Phelps demonstrates the influence of the Habsburg government on the integration of the United States into the nineteenth-century Great Power System and the influence of American racial politics on the Habsburg Empire's conceptions of nationalism and democracy. In the crisis of World War I, the U.S.-Habsburg relationship transformed international politics from a system in which territorial sovereignty protected diversity to one in which nation-states based on racial categories were considered ideal.