In most accounts of peacemaking after World War I, “flawed” decisions at “Versailles” caused the ethnically mixed states of Central and Eastern Europe to descend into violent ethnic clashes, while the allegedly more homogenous Western European states faced few issues with minorities. This article challenges this simplistic view by examining the treatment of German-speaking minorities in the borderlands of Alsace-Lorraine, South Tyrol, and Eupen-Malmedy between 1918 and 1923 in the immediate post-war and the early interwar period. Building on an innovative comparative framework of five key variables, we find that, in all three cases, post-war borders generated incentives for the respective governments to suppress their new minorities, and that states used ethnic markers to target them. The strength of state institutions and liberal principles account for a reversal (Alsace-Lorraine), moderation (Eupen-Malmedy), or hardening (South Tyrol) of measures. International commitment to defend the new borders and the absence of a tradition of ethnic conflict also had a significant impact.