Over the past century, democracy spread around the world in turbulent waves of reform that swept across national borders. Yet these cascades often failed, cresting and rolling back into autocracy. Aftershocks offers a new global-oriented explanation for this wavelike spread and retreat - not only of democracy but also of its twentieth-century rivals, fascism and communism.Seva Gunitsky argues that waves of regime change are driven by the aftermath of cataclysmic disruptions to the global order. These hegemonic shocks, marked by the sudden rise and fall of great powers, have been essential and often-neglected drivers of domestic reforms. Though rare and fleeting, they also create a chance for sweeping institutional changes - by triggering military impositions, by exogenously shifting the incentives of domestic actors, or by transforming the very basis of political legitimacy itself. As a result, the evolution of modern regimes has been deeply linked to clashes among great powers, who repeatedly - and often unsuccessfully - sought to cajole, inspire, and intimidate other states into joining their camps.