The idea of modern terrorism and the practice of terrorist violence emerged in Britain’s first colony, Ireland, before spreading through imperial networks to South and East Asia, to Africa, and to the Middle East. Thus, empire not only birthed terror, but also made it global. And the sheer spread, diversity, and longevity of that empire produced multiple stages in the evolution of terrorism from rural intimidation to urban guerilla warfare to homegrown radicalism. Indeed, today’s global terror challenges—the ethics of counter-terrorism, the threats of Islamist and international terrorism, and the rise of homegrown right-wing extremism—all have roots in colonialism.