This article reviews some of the milestones of thinking about political radicalization, as scholars and security officials struggled after 9/11 to discern the precursors of terrorist violence. Recent criticism of the concept of radicalization has been recognized, leading to a 2-pyramids model that responds to the criticism by separating radicalization of opinion from radicalization of action. Security and research implications of the 2-pyramids model are briefly described, ending with a call for more attention to emotional experience in understanding both radicalization of opinion and radicalization of action.
McCauley, Clark and Sophia Moskalenko. 2017. "Understanding Political Radicalization: The Two-Pyramids Model." American Psychologist 72 (April): 205-216. http://psycnet.apa.org/journals/amp/72/3/205/