Counterinsurgency originated in British military and foreign policy during the 1940s. It later emerged as a showcase strategy among American foreign policy advisers and military strategists in the early 1960s. Eventually, it evolved into a major component of cold war strategy, and what became known specifically as “counterinsurgency theory” played a significant role in the planning of the American war in Vietnam. The Vietnam War forced planners to become far more sober minded about the limitations of the theory, but many of its general principles, nonetheless, found their way into cold war applications for years to come and contributed to the intellectual groundwork of 21st-century counterterrorism efforts.