No single event explains all recent and current examples of religious terrorism. Samuel Huntington’s highly influential yet very controversial argument is however a good place to start, not least because it highlighted probably the most egregious example of the genre, Islamic terrorism. Although Huntington was discussing what he called “clash of civilisations,” this did not mean that inter-religious or inter-cultural clashes were not also in focus. This chapter focuses on the development of “religious terrorism” after the end of the Cold War. It argues that religious terrorism has affected global security and led the USA into various unsuccessful foreign policy adventures—into Iraq, Afghanistan, and so on. In addition, religious terrorism stimulated the rise—and fall—of various transnational Islamic terror groups, as well as contributed to the fragility of various states, including: Somalia, Nigeria, and Mali.