This study seeks to determine which factors affect an ethnonational group's decision to utilize terrorism. Current political theories have proposed several answers, but the theoretical underpinnings of those answers are both disparate and weak. Thus, in answering this question, a new model of terrorism is necessary, one which spans the four primary levels of analysis but grounds it all in the actor: the individual. The book first examines the existing literature concerning the causes of terrorism. These threads are then woven into a single theory—based on the individual—explaining why the known correlates of terrorism increase the chance that an ethnic group will resort to terrorism: The Pressure Model. Several derivative hypotheses are then tested using modern statistical methods, including complementary log-log cross-sectional time-series regression. Finally, the book discusses several recommendations from the theory that should inform policy in both international and domestic spheres. Professionals in the field of terrorism policy as well as policymakers, academics, and students interested in the causes of a group’s path into terrorism should find much of interest in this book.