This chapter sets out why a history of Ulster loyalism in the three counties after partition matters and outlines the literature on ethnic conflict, Ulster loyalism, and terrorism and political violence in Ireland. The chapter then sets out the book’s two main arguments. First, memories of the violence experienced by one generation of Protestants in the three counties entrenched a sense of separation from the new Irish state on the part of subsequent generations. Intergenerational grievance and inter-communal distance kept loyalism alive and set the conditions for militancy and revenge in the future, including during the Troubles. Three-county loyalists played an important role in Ulster loyalist militant movements in Northern Ireland after partition.