The sociology of violence still struggles with two critical questions: What motivates people to act violently on behalf of groups and how do they come to identify with the groups for which they act? Methodologically the article addresses these puzzling problems in favor of a relational sociology that argues against both micro- and macro-reductionist accounts, while theoretically it proposes a twofold reorientation: first, it makes a plea for the so called cognitive turn in social theory; second, it proposes following praxeological (...) accounts of social action that focus on the dynamic interpenetration of cognition and socio-cultural practices. The argument is that symbolic boundaries constitute the “missing link” that allows for overcoming the micro-macro gap in violence research: Symbolic boundaries can cause people's participation in collective violence by providing the essential relational resources for violent action and by triggering the cognitive/affective mechanisms necessary for social actors to become drawn into mobilization processes that can cause their engaging in coordinated attacks on sites across the boundary. The article offers a new theoretical argument by drawing on knowledge from violence research, social action theory and cognitive science allowing for a non-reductionist theory of action that explains how and why people engage in collective violence. (shrink)