Since the terrorist attacks of 9/11, scholars, practitioners, and policymakers alike have become increasingly interested in understanding the factors that drive various forms of violent extremism. This heightened focus is anchored in broader trends of extremism. For instance, while the number of terrorist attacks has declined by approximately 25 percent since its zenith in 2015, the number of fatalities due to terrorism has reached its highest point since 2017 (Institute for Economics and Peace, 2024). The psychological factors and processes that underpin extremism and radicalization are particularly central to understanding the drivers of violent extremism and have been researched intensively over the past decades. Many high-impact journals have encouraged submission of manuscripts focused on understanding political violence and extremism, as the need to understand this phenomenon remains a pressing social issue. However, a comprehensive handbook that makes this broad knowledge accessible to various audiences was missing. Therefore, our ambition with this handbook was to create the number one go-to resource for researchers, practitioners, policymakers, and students interested in understanding the psychology of violent extremism.
1.1 Target Audience and Focus on Intervention and Prevention
When we planned this handbook, a vital aspect was that it should address the needs of scholars (at different levels), policymakers, and practitioners alike. The handbook is an essential resource for new and established scholars in psychology as well as related disciplines (e.g., international relations, political science, criminology, sociology) who study extremism and other forms of collective/political action. Our aim was to make this handbook accessible to scholars at various stages of their careers while ensuring its utility for each group. Almost all chapters include visual representations of models and theories, which aid in guiding the reader’s understanding. These visual aids help to clarify complex concepts and provide a tangible reference that can enhance comprehension and retention of the material. At the same time, the chapters needed to offer novel syntheses and extensions of the authors’ previous work. We are pleased to report that all chapters present unique and new perspectives in this handbook. These contributions push the boundaries of current research, offering fresh insights and proposing new frameworks that advance the field of violent extremism studies.
Beyond its academic focus, our handbook is essential for practitioners and policymakers who work to prevent radicalization and violent extremism. To maximize the handbook’s utility for this audience, we asked all authors to concretely formulate how their insights can improve the societies we live in. Therefore, each chapter (except for Chapter 3, which given its scope, provides recommendations primarily for researchers) contains a section called “Implications for Practitioners and Policymakers” that specifically discusses how the respective psychological approach or theory can help reduce violent extremism, for instance, by informing interventions, deradicalization, and prevention.
1.2 The Handbook’s Structure
An inherent part of the handbook is its focus on different levels of analysis and its comprehensive scope. That is, instead of concentrating on one level of analysis or a limited set of theoretical perspectives, the ambition of the handbook was to cover all the major perspectives at the definitional, individual, group, and contextual/macro levels. Violent extremism is a complex and multidimensional phenomenon that requires an analysis of factors across multiple levels to be fully understood. The handbook is therefore organized into four parts, each focusing on different levels of analysis. It is crucial to acknowledge that the value of each chapter lies in its ability to link the phenomena under study to processes occurring at multiple levels. Therefore, the structure of the book is designed to facilitate an effective framework for understanding these complex interactions, rather than rigidly categorizing factors at a specific level. In practice, many of the factors discussed are concurrently present at various levels.
1.2.1 Part I: Concepts, Definitions, and Trends
The book commences with a section dedicated to concepts, definitions, and trends. The precise definitions of violent extremism, and its subforms such as terrorism, remain a subject of contention among social scientists. Also, policymakers and practitioners frequently employ diverse conceptualizations owing to different national or regional laws and the definitions provided by governmental entities. Chapter 2 therefore provides comprehensive and universally applicable definitions to guide the content of the handbook, inform policymaking, and facilitate future research. It explores the various ways in which violent extremism has been defined and its conceptual overlap and distinctions from related concepts such as radicalization and terrorism. Notably, to accommodate the diversity of perspectives, authors of subsequent chapters were afforded the freedom to deviate from these definitions by defining violent extremism in ways that are coherent with their overarching frameworks.
Chapter 3 provides a machine-learning overview of the entire field of violent extremism, analyzing over 34,000 articles. This chapter uses techniques like topic modeling to identify key trends, revealing two primary waves of research from 1950 to 2024 and a diversification in studied groups, contexts, and topics. Political science, international relations, psychology, history, and law emerge as the top contributing fields, with political science leading since the 1970s. The chapter emphasizes the need for methodologies that allow causal inferences, recommends incorporating state-based perspectives, utilizing big data, and focusing on developmental research to improve the quality of violent extremism studies.
1.2.2 Part II: Individual-Level Perspectives
Having established a foundation in terms of definitions and provided data-driven insights into developments and needs in the field, the handbook progresses to the second major section, which focuses on individual-level perspectives on violent extremism. Chapter 4 looks at the role of psychopathology and personality traits. In light of limited empirical support, a lack of scientific rigor, and methodological shortcomings, many scholars disregarded psychopathological explanations of violent extremism in favor of situational explanations. However, recent findings show that the odds of some psychopathologies are higher among some violent extremists. This chapter reviews the existing research and explains when and why psychopathology is causative in violent extremism and radicalization. Next, it focuses on the importance of nonclinical personality traits that historically have been overlooked in research on violent extremism. Reviewing recent research, the chapter demonstrates how basic personality traits can to some extent explain people’s engagement in different types of violent extremism.
Whereas there is a general agreement that there is not one profile that characterizes violent extremism, Chapter 5 identifies a set of extremist (arche)types – widely recognized in criminology and political sciences but notably underexplored in the psychological examination of violent extremism. Drawing on comprehensive fieldwork and interviews with violent extremists, this chapter delineates five predominant archetypes that characterize various extremists: the “ideologists,” “followers,” “adventurers,” “misfits,” and “traditionalists.” The chapter describes in detail the distinct pull, push, and barrier factors influencing each archetype.
Chapter 6 focuses on the role of gender in violent extremism, especially in an era marked by significant political mobilization around family policies and gender issues. The chapter explores key issues like masculinity, including the incel movement and the manosphere, as well as femininity, female extremist violence, and the gendered dimensions of prevention. It outlines the various ways in which gender intersects with violent extremism.
Anecdotal observations suggest that people who have lost meaning in life and feel insignificant are more likely to engage in violent extremism. Chapter 7 reviews research demonstrating how a quest for significance – a motivational state where individuals want to matter and be respected – can drive violent extremism. It outlines various factors that may contribute to this quest and determine the circumstances under which it leads to violent outcomes.
Whereas religion has been implicated in incidents of extremist violence in most parts of the world, research has been contradictory regarding its role. Chapter 8 dissects the intricate relationship between religious fundamentalism and violent extremism, emphasizing the socio-cognitive processes that drive radicalization. It identifies how religious fundamentalism can foster violent extremism through various group-related factors and ideologies but also highlights that this progression is contingent upon specific situational and contextual factors, such as perceived injustices and threats.
Chapter 9 addresses a factor that has been anecdotally linked to motivations for violent extremism but has predominantly garnered attention only in recent years: the belief in conspiracy theories. It discusses theoretical explanations for this link and the mechanisms that might underpin it, and provides a summary of the empirical evidence categorized into three main research strands: findings from radicalized groups and individuals, data from general population studies on support for and intentions to engage in violent extremism, and studies on extreme political attitudes in the general population.
Exploring the connection between moral beliefs and violent extremism, Chapter 10 addresses the limited empirical research directly linking these two areas. It reviews various scholarly approaches that may inform this relationship, either directly or indirectly, and proposes multiple conceptual frameworks to further investigate this nexus in the future. These frameworks include moral foundations theory, sacred values, parochial altruism, honor culture, moral universalism, clashing moralities, and the ethical-dilemma (trolley cases) paradigm, which are applied to understanding violent extremism in the social sciences.
Chapter 11, the final chapter of the individual-level part of the handbook, explores the role of emotions in fostering violent extremism, utilizing insights from research on emotional drivers of violent intergroup behavior. It discusses how emotions are shaped by cognitive appraisals of events and influenced by social identities and group dynamics in the context of intergroup hostility. The chapter highlights specific emotions at different stages of radicalization: preradicalization emotions like humiliation, shame, and anger that fuel a desire for justice and self-image restoration; active radicalization emotions such as contempt, disgust, and hatred that promote exclusion and eradication of targets; and engagement stage emotions like love, joy, and pride that enhance commitment and motivate others.
1.2.3 Part III: Group-Level Perspectives
The third section of the handbook consists of various chapters that are most appropriately positioned at the group level, as they deal with group perceptions, attitudes, and inclinations. The first three chapters examine how our perceptions of groups and our beliefs about how intergroup relations should ideally be structured can function as antecedents to violent extremism. Social identity is the topic of Chapter 12 in this section. The chapter utilizes social identity theory and uncertainty-identity theory to explain how normal group behaviors can escalate into violent extremism, emphasizing that social identity processes are motivated by the desire for a favorable self-concept through high-status group membership and the need to reduce self-uncertainty through clear group identities.
Chapter 13 examines scenarios where issues related to group dynamics become deeply personal. It describes identity fusion – a profound commitment to a group, leader, or set of beliefs – and its role in driving individuals across diverse cultures and ideologies to perform extreme behaviors. It thoroughly discusses the concept, nature, origins, and outcomes of identity fusion, how it is measured, and the dynamics that enhance or mitigate its impact. The chapter also reviews research on identity fusion among individuals at various stages of radicalization and among combatants.
Chapter 14 effectively merges individual-level and group-level perspectives to explore the psychosocial factors driving violent extremism and conflict. It discusses how sacred values, identity fusion, and social dynamics underpin the devoted actor framework, contrasting with rational actor models. This integrated analysis reveals how deeply held beliefs and group affiliations inspire and sustain the will to fight, amid the backdrop of global terrorism and polarizing sectarian nationalism.
Chapter 15 analyzes why individuals resort to political violence, exploring whether their motivations stem from a desire to enforce group dominance or promote equality and whether they view the existing intergroup power structures as legitimate or illegitimate. It identifies four potential goals of political violence based on these motivations: maintaining the current social hierarchy, reducing inequality, reshuffling the structure of group-based dominance, or preserving an oppressed group’s dominance for its protection. The discussion extends to redefining extremist violence, not by normative standards or the identity of the actors (governmental or otherwise), but by whether the actions contravene fundamental principles like human rights and international humanitarian law.
The next three chapters explore how perceptions of one’s own group and others can contribute to violent extremist outcomes. Chapter 16 highlights relative deprivation – the perception that one’s group is unfairly deprived compared to others – as a critical factor eliciting support for violent extremism, stressing that this perception can arise in both disadvantaged and advantaged groups, especially when they see no normative solutions to their grievances. The chapter proposes an integrative model linking group-based relative deprivation to violent extremism under various conditions.
Various types of intergroup threats – symbolic, realistic, numerical, existential, and meta-threat – and their role in fostering violent extremist attitudes, intentions, and behaviors, are the topic of Chapter 17. It reviews theoretical perspectives and synthesizes empirical findings to demonstrate how perceived threats can lead to extreme out-group hostility and violent responses in both majority and minority groups across different cultural contexts. These perceptions, often shaped by cultural narratives, media portrayals, and political rhetoric, can escalate the radicalization process.
Chapter 18, the final chapter in the group section of the handbook, explores the concept of dehumanization, which characterizes certain social groups as inferior to the human ideal, and its link to violent behavior by easing moral constraints. It examines both traditional and modern approaches to measuring dehumanization in psychological research, reviewing its role not only as a precursor to violence but also how violence can lead to further dehumanization, creating a cyclical reinforcement between the two. The discussion also covers the dehumanization of extremists versus by extremists and introduces the concept of meta-dehumanization – believing that one’s group is dehumanized by others – as a catalyst for continued violence.
1.2.4 Part IV: Macro-Level Perspectives
Moving from the group to the macro level, the upcoming chapters highlight the importance of understanding violent extremism through individuals’ position within societal structures, both national and international. Chapter 19 challenges reductionist views on the role of poverty in violent extremism by advocating for a “from societies to cells” approach. It utilizes the metaphor of a staircase to terrorism to illustrate the societal conditions that increase the likelihood of individuals progressing toward terrorist actions, each step marked by specific psychological processes and dominated by subjective experiences. While actual material conditions do not directly predict an individual’s movement up the staircase, perceptions of relative deprivation and injustice significantly contribute to such a progression. Additionally, while social class and poverty alone do not determine this upward movement, they influence where on the staircase certain terrorist specializations occur.
Chapter 20 delves into the impact of international military interventions and foreign military occupations on violent extremism, with a focus on the psychological processes of radicalization and subsequent patterns of political violence they may ignite. It starts by reviewing significant literature, which suggests that such interventions and occupations often exacerbate grievances and feelings of national humiliation, thereby increasing support for political violence among affected populations. The chapter also explores how these actions contribute to violent extremism by encouraging the othering of foreigners, deteriorating human rights standards, and creating strategic environments favorable to political violence. Additionally, it examines the concept of vicarious radicalization, where interventions and occupations can incite political violence beyond the borders of the directly affected countries.
Chapter 21 discusses how globalization, as a powerful transformative force, impacts modern societies, highlighting both the disruptions to traditional sociocultural norms and the exacerbation of inequalities under its neoliberal influences. It outlines how globalization challenges fundamental human needs such as local embeddedness and security, fostering perceptions of threat that can lead to extreme psychological reactions and potentially violent extremism. The chapter emphasizes that while the manifestations of such extremism can vary globally, they are interconnected and often amplified by online platforms, resulting in increased polarization.
The intricate relationship between climatic catalyst events and violent extremism is discussed in Chapter 22, focusing on how the increasing severity and frequency of climate-induced disasters like hurricanes, tsunamis, droughts, and wildfires can foster conditions conducive to extremism. It details how the climate crisis amplifies several risk factors globally, such as feelings of insignificance, reduced opportunity costs, mass migration, and defensive reactions that may align with ecofascist ideologies. The chapter further explores the climate change and violence model, illustrating a feedback loop where climatic events escalate violence and associated risk factors. Two case studies underscore the connection between specific climate shocks and resultant violent extremism.
Chapter 23, the last chapter in this macro-level section, introduces an integrated temporal approach to understanding the psychology of violent extremism, emphasizing the role of memory and future imaginings in motivating current violent behaviors. It discusses how nostalgic reminiscences of a perceived glorious past can amplify feelings such as relative deprivation and collective angst, while memories of historical injustices can instill a sense of moral entitlement to use violence. Additionally, the chapter explores how visions of the future – either utopian or dystopian – can mobilize individuals toward violent extremism by providing legitimacy and urgency to their actions, or conversely, how positive future outlooks can act as deterrents against radicalization.
1.3 Ensuring Rigor, Balance, and Diversity in the Chapters
All chapters in this handbook have undergone multiple rounds of rigorous review to ensure adherence to high scientific standards. During the review process, special attention was given to content quality and avoiding common biases in the field of violent extremism. It was particularly important to ensure that the chapters presented a balanced perspective, acknowledging the diversity among violent extremist groups and actors. For example, the chapters collectively discuss cases from and implications for right-wing, left-wing, and Islamist extremism, avoiding an undue focus on any single form.
Ensuring diversity among our contributors was of paramount importance. Although we had aimed to include more authors residing in non-Western regions severely affected by violent extremism, a substantial number, including one of the handbook editors, originate from non-Western regions, and their insights considerably enhance the scope of this handbook. The volume also showcases a variety of research perspectives. While it primarily concentrates on the psychology of violent extremism, the handbook adopts an interdisciplinary approach, incorporating perspectives that utilize diverse data sources. Consequently, sociologists, criminologists, and political scientists contribute to the chapters where their insights are directly relevant to psychological interpretations.
In summary, this handbook represents a collective endeavor to elucidate the multifaceted nature of violent extremism through a comprehensive psychological lens. Our contributors, spanning diverse disciplines and backgrounds, offer pioneering insights and practical guidance, ensuring that this resource meets the complex needs of scholars, practitioners, and policymakers alike. By integrating varied levels of analysis and extending the frontier of current research, we aim to foster a deeper understanding of the psychological underpinnings of extremism and to contribute meaningfully to its prevention and mitigation. We trust that the chapters herein will not only inform and inspire but also catalyze further scholarly inquiry and practical action against the backdrop of a rapidly changing global landscape. With this foundation, we invite our readers to explore the nuanced perspectives and innovative frameworks that follow, each contributing a vital piece to the intricate puzzle of violent extremism.
