“Rebel City” investigates how the city of Fiume (now located in modern-day Croatia and known by its Croatian name, Rijeka) rebelled collectively against the dictums of Great-Power politics in the immediate aftermath of World War I. This project argues that the longevity of the city’s challenge to Versailles diplomacy cannot be understood as a simple consequence of the will the city’s charismatic leader, but instead as a marker of the relative strength a centuries-old city-state had in a continent of not-yet-effective nation-states. This research promises both to contest previous histories of the Fiume crisis itself as well as to question common understandings of who the most effective political actors were in a postwar Europe newly rid of empires but not yet settled into nation-states.