Over the last 10 years, the concept of cumulative extremism (CE) has gained currency amongst both academics and policy-makers. Despite this, there is a dearth of empirical research into the idea. Furthermore, the extant literature – which has focused primarily on conflicts between social movements and groups in England – has not drawn firm conclusions into how and why processes of CE might develop. This paper will address this gap in the literature by examining the Troubles in Northern Ireland from its onset in the 1960s through to its peak as a lethal M/CM contest in 1972. In so doing, it aims to both improve the understanding of CE as well suggesting policy measures which might be employed to interrupt the escalation of movement–countermovement conflicts.