The 1920 Schleswig plebiscite, conducted under Wilsonian principles of national self-determination, fixed the present Danish–German border and has often been hailed as a model of peaceful conflict settlement. Unlike partitions marked by mass expulsions or violence, the Schleswig process avoided forced population transfers and provided the basis for minority rights regimes later enshrined in the Bonn–Copenhagen Declarations of 1955. Yet the vote also fractured a long-standing zone of cultural and political overlap, compelling inhabitants to align with either Denmark or Germany and leaving roughly one-fifth on the “wrong” side of the frontier. This division severed deep-rooted cultural and economic networks, with towns such as Flensburg entering prolonged decline. Schleswig’s case underscores the paradox of border plebiscites: celebrated internationally as exemplars of orderly resolution, they often engendered local dislocation, economic hardship, and the erosion of regional identities. In this tension, Schleswig reveals both the promise and the tragedy of border reconfiguration in twentieth-century Europe.