Numerous scholars have investigated religiously motivated violence, particularly in the wake of September 11, including discussions on the role of modernity in triggering religious violence, the increasing presence of religion in politics, the violence-prone nature of certain religions, and religion's correlation with ethnicity and other conflict-intensifying variables. However, religious activism and violence are not new phenomena. Few theories have been advanced that move across time and space and, broadly, seek to explain the conditions under which religion becomes involved in activism and violence. This article argues that three broad causal arguments for religious activism—social movements, fundamentalism, and apocalyptic warriors—help explain the conditions under which religiously motivated violence occurs across time and space. These three causal arguments offer a spectrum of goals within religious activism, ranging from challenging social practices and government policies, to defending specific interpretations and practices of the faith, to hastening the apocalypse. Furthermore, each of these theories proposes different ways that religion becomes involved in social, political, and religious activism and the conditions under which groups use violence to further their goals. The article concludes by suggesting countermeasures for each type of religious activism.