Oppositional violence and repression are closely related. In fact, repression often produces an escalation of violence rather than controlling it. Bridging social movement studies and research on violence, the article uses a small-N, most-different research design to analyse the working of a specific mechanism at the onset of different types of political violence: escalating policing. In particular, it indicates specific causal mechanisms, related to interactions between social movements and the state, which create the conditions for some splinter groups to move underground. In order to compare left-wing, right-wing, ethno-national and religious violence, the article presents empirical references to the author's own empirical research on Italy and the Basque Country as well as a secondary analysis of the conflicts that preceded the rise of al-Qaeda.