Nationalism and the puzzle of reversing state size

Having increased for centuries, territorial state size began to decline toward the end of the nineteenth century and has continued to do so. The authors argue that processes triggered by ethnic nationalism are the main drivers of this development. Their empirical approach relies on time-varying spatial data on state borders and ethnic geography since the nineteenth century. Focusing on deviations from the nation-state ideal, the authors postulate that state internal ethnic fragmentation leads to reduction in state size and that the cross-border presence of dominant ethnic groups makes state expansion more likely. Conducted at the systemic and state levels, the analysis exploits information at the interstate dyadic level to capture specific nationalist processes of border change, such as ethnic secession, unification, and irredentism. The authors find that although nationalism exerts both integrating and disintegrating effects on states' territories, it is the latter impact that has dominated.