Over the past century, Great Power transitions have led to the spread of autocracy in two distinct ways. First, the sudden rise of autocratic Great Powers led to waves of autocracy driven by conquest but also by self-interest and even admiration, as in the fascist wave of the 1930s or the post-1945 communist wave. Second, the sudden rise of democratic hegemons led to waves of democratization, but these waves inevitably overextended and collapsed, leading to failed consolidation and rollback. While these two categories - rollback from democratic overstretch, and hegemonic authoritarian cascades - both look like autocratic diffusion, they stem from very different causes. This chapter examines the relationship between Great Power transitions and regime diffusion. A key question is whether modern democratic decline is a post-1991 correction – that is, the delayed but inevitable overstretch of the post-Soviet wave – or the beginning of a distinct new wave of autocracy.