Fear of transnational terrorism, along with a revitalization of sectarian nationalism, is sundering social and political consensus across the world. Can psychology help? The focus of this review is on the psychological and related social factors that instigate and sustain violent extremism and polarizing group conflict. I first describe the changing global landscape of transnational terrorism, encompassing mainly violent Islamist revivalism and resurgent racial and ethnic supremacism. Next, I explore the psychosocial nature of the devoted actor and rational actor frameworks, focusing on how sacred values, identity fusion, and social network dynamics motivate and maintain extreme violence. The psychology of the will to fight and die is illustrated in behavioral and brain studies with frontline combatants in Iraq, militant supporters in Morocco, and radicalizing populations in Spain. This is followed by a consideration of how to deal with value-driven conflicts and a discussion of how the Internet and social media encourage the propagation of polarized conflict.

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