Systematic review: Risk factors and mechanisms of radicalization in lone-actor grievance-fueled violence

Abstract The purpose of this systematic review is to identify risk factors and mechanisms of radicalization associated with lone-actor grievance-fueled violence. In this paper, I focus on five violent lone-actor “types”; lone-actor terrorists, workplace attackers, school shooters, rampage shooters and violent Incels. Data synthesis of the 78 included studies led to the identification of nine risk factors: 1) sociodemographic background; 2) social ties; 3) interpersonal rejection; 4) mental illness; 5) subclinical personality traits; 6) strain; 7) grievances; 8) emotional traits and states; and 9) cognitive processes and content. As a limitation of the extant literature is the lack of a coherent and integrative framework of how each factor relates to the others, findings were re-synthesized to show how risk factors essentially reflect five generic social and psychological mechanisms of radicalization: socialization, small-group dynamics, psychological need restoration, mental health from a dimensional perspective, and mechanisms of moral disengagement. The paper ends with a discussion of this framework and its implications for future research on lone-actor grievance-fueled violence.