Scholars, observing clustering in transitions to democracy, argue that democratization diffuses across borders as citizens in autocracies demand the same reforms they witness in neighboring states. We disagree. This article demonstrates that diffusion plays only a highly conditional role in democratization. We advance and test an alternative two-step theory of clustered democratization: (1) economic and international political shocks, which are clustered spatially and temporally, induce the breakdown of authoritarian regimes; then (2) democratic diffusion, in turn, influences whether a fallen dictatorship will be replaced by a democracy or a new autocracy. Diffusion, despite playing an important role, is insufficient to explain the clustering of transitions. Using data on 125 autocracies from 1875 to 2004, we show that economic crises trigger authoritarian breakdowns, while diffusion influences whether the new regime is democratic or authoritarian.