The political scientist Samuel Huntington famously depicted the spread of democracy over the last two centuries as a series of “waves”: periodic moments when many countries jumped more or less simultaneously on the democratic bandwagon. In this landmark study, Gunitsky goes further and illuminates the deep connections between global shifts in power and waves of domestic regime change. His book reveals how a series of geopolitical disruptions in the twentieth century created “hegemonic shocks” that triggered movements across the globe toward or away from democracy. In the aftermath of the two world wars and after the end of the Cold War, the United States and western European states became hegemonic powers and catalyzed independence movements and democratic transitions. The rise of German power in the 1930s spurred shifts toward fascism elsewhere, and the emergence of Soviet power in the 1940s led to a raft of communist insurgencies and Soviet-backed regimes. No book has made a stronger case that the fate of democracy is tied to the rise and fall of great powers and the leadership of liberal hegemonic states.