Center-periphery explanations focus on political centralization, state collapse, and nationalization to explain the genesis of separatist movements that form new national states. This study shows that three periods of Chinese-Mongolian relations-land reform (1900-1911), revolution and interregnum (1912-16) and warlordism (1917-30)-contained events that center-periphery perspectives associate with the rise of autonomous movements, yet Mongolian separatism did not occur until the last period. To explain this puzzle, the author characterizes the formation, integration, and dismemberment of the frontier governance system as an intermediate body between the center and the periphery. She demonstrates that the effects pointed to by center-periphery explanations were mediated, at least in the case of Inner Mongolia, by the structural transformations of the frontier governance system. Not assuming a natural opposition between the center and the periphery, this study elucidates the polarization of the center-periphery relationship and its impact on minority separatism. This article explains the timing of Mongolian separatism within the context of Chinese imperial dissolution in the early 20th century. Mongols were the most powerful and important minority allies of the Qing Empire (1644