Replication Data for: Nationalism and the Puzzle of Reversing State Size

Having increased for centuries, territorial state sizes began declining towards the end of the 19th century and have continued to do so until today. We argue that processes triggered by ethnic nationalism are the main drivers of this development. Our empirical approach relies on time-varying spatial data on state borders and ethnic geography since the 19th century. Focusing on deviations from the nation-state ideal, we postulate that state internal ethnic fragmentation leads to reductions in state sizes and that the cross-border presence of dominant ethnic groups makes state expansion more likely. Conducted at the systemic and state levels, our analysis exploits information at the interstate dyadic level to capture specific nationalist processes of border change such as ethnic secession, unification, and irredentism. We find that while nationalism exerts both integrating and disintegrating effects on states’ territories, it is the latter impact that has dominated.