Workers of the world, unite! Franchise extensions and the threat of revolution in Europe, 1820-1938

•Unique measure of threat of revolution.•New evidence on the link between threat of revolution and democratization.•Unique historical data•New theory of international diffusion of information about revolutions and suffrage reform.

We test the hypothesis that the extension of the voting franchise in Europe was related to the threat of revolution. We contend that international diffusion of regime contention and information about revolutionary events happening in neighboring countries generate the necessary variation in the perceived threat of revolution. Using two samples of European countries covering the period from 1820 to 1938, we find robust evidence which is consistent with the 'threat of revolution hypothesis'. We also find some evidence that war triggered suffrage reform.