Research spanning the globe including samples of current terrorists, former terrorists, individuals at risk of radicalization, and combatants against terrorism has shown that identity fusion – that is, a visceral feeling of commitment to a group, leader, or set of convictions – propels individuals to engage in extreme behaviors on behalf of the fusion target across cultural and ideological boundaries. From jihadist radicals to ethnonationalist terrorists and neo-Nazis, the behavior of violent extremists is permeated by the effects of identity fusion, underscoring the need to understand this construct for the development of enlightened measures to counter violent extremism. In the present chapter, we provide a comprehensive review. We introduce the concept of identity fusion and explain its nature, antecedents, and behavioral consequences. We also summarize how it can be assessed, the mechanisms that amplify or reduce its effects, and the processes responsible for its behavioral impact. After that, we provide an overview of existing identity fusion research with individuals at different stages of the radicalization process and fighters and highlight its implications for the development of tools to assess the risk of radicalization and measures to prevent violent radicalization and promote disengagement from violence.

Fear of transnational terrorism, along with revitalization of sectarian nationalism, continues to sunder social and political consensus across the world and encourage violent conflict. The focus here is on psychosocial factors that instigate and sustain violent extremism and polarizing group conflict. I describe the changing global landscape of transnational terrorism, encompassing mainly violent theocratic revivalism, and resurgent racial and ethnic supremacism wherein perceived threats to a dominant group’s core values lead to extremist reactions against feared replacement via minority and immigrant populations. Next, I explore the psychosocial nature of the rational actor versus devoted actor frameworks. Analysis centers upon how sacred values such as God or country, identity fusion with a group or idea, perceptions of spiritual strength overriding material strength, and social network dynamics motivate and maintain absolutist attitudes and support for violence whatever the risks, costs, or consequences. The psychology of the will to fight and die is illustrated in behavioral and brain studies with combatants and civilian populations in the Middle East, North Africa, Europe, and North America. This is followed by considering how the internet and social media encourage propagation of polarized conflict, and how societies and policymakers might better deal with violent, value-driven extremism.