The violent turn in non-violent collective action: What happens?

Collective actions (e.g., protest marches, social movements) that begin peacefully sometimes turn into violent clashes between demonstrators and police, with alarming consequences. Research on the violent turn, informed by intergroup social psychology and micro-sociology, has made significant but separate advances. We review them jointly to form an integrated, fuller understanding of the violent turn and promote interdisciplinary dialogue by discussing their respective strengths and identifying areas where they complement each other. For these purposes we first extract from the psychology of interpersonal aggression literature a three-phase temporal pattern of aggression escalation to provide a common reference for reviewing representative studies and theories in intergroup social psychology (e.g., elaborated social identity model of crowd rioting, intergroup emotions theory) and micro-sociology (e.g., micro-sociological theory of violence, emotional dynamics and behavioural dynamics). The results of our analysis show a sequence of events beginning from instigators and their impellance in the early phase of the violent turn, psychological transformations forming a proclivity to aggress in the middle phase, and collective empowerment that disinhibits violence in the late phase. Group power and, to a less extent, group emotions permeate all phases. The sequence of events reveals transitional points where intervention may be applied to avert or abort violence.