This chapter argues that throughout history many religions have proved themselves capable of sparking and fueling hostility toward outsiders and even toward people in the same faith who are viewed as unacceptable for one reason or another. We examine recent manifestations of extremism in Christianity, Hinduism, Buddhism, Judaism, and Islam, explaining that analysts often disagree about the extent to which religious beliefs and institutions are causally important. Key terms such as religious extremism, fundamentalism, radicalization, and terrorism are defined, noting the crucial importance of maintaining a distinction between the religious extremist and the extremely religious. Though we suggest researchers face many methodological challenges, we explore a broad range of empirical studies on related topics. The chapter also reviews theory and research on why and how people become religious extremists. We further draw on the psychology of radicalization, arguing that nowadays most scholars believe that there are cognitive and behavioral processes at work. Some people may move directly to carrying out terrorist deeds without acquiring much group ideology or religious belief.

Radicalization is most often seen as a gradual process that may or may not lead to radical or extreme behaviors such as terrorism. Theories on the radicalization process often highlight the potential role of social exclusion in the propensity for radicalization. We here present some of the major radicalization theories and discuss exclusion as a common denominator that could trigger a radicalization process. We then describe the research on personality and individual differences in relation to radicalization briefly, before discussing individual differences that are connected to exclusion in more depth. We go through the available empirical evidence supporting the notion that some individual level differences, such as rejection sensitivity, could moderate the effect of exclusion on radicalization. We further discuss other potential individual differences that relate to exclusion such as need to belong and entitlement.

White extremism has been a rising trend in North American and European countries over the past two decades. Despite the systemically engrained privileged status of people who identify as white in US society, one of the causes of white extremism is a perceived threat of being sidelined/disadvantaged by individuals with non-white identities. For example, the mainstreaming of the great replacement theory among right-wing media outlets and politicians demonstrates this perception. We examine this perception, and white extremism rhetoric and radicalization broadly, within the context of social exclusion at both the individual and systemic levels. We further embed this analysis within theories and research focused on concepts of “the self,” social identity, and related psychological needs usually impacted by social exclusion. We recommend researchers and practitioners interested in extremism and radicalization to intentionally consider self-related theories and constructs going forward.

Both ostracism experiences and conspiracy beliefs have been discussed as formative ingredients of radicalization trajectories and violent extremism. The present chapter provides a brief introduction to the psychology of conspiracy beliefs and the connections made to violent extremism. In its central part, it discusses the connection between the two in discussing (1) direct evidence for ostracism experiences increasing conspiracy belief, (2) indirect evidence via highlighting how the four fundamental needs postulated to be threatened by ostracism have also been connected to conspiracy beliefs, and (3) a discussion of the reverse causation of expressing conspiracy beliefs leading to being ostracized. In all sections, specific emphasis will be dedicated to the question of how reliable and strong the available evidence is, with experimental evidence weighing heavier than correlational evidence and repeatedly replicated and meta-analytically robust effect weighing heavier than single demonstrations.

Societies have constant competition between progressive forces that would reduce group-based inequality and regressive forces that would maintain it. As groups vie for superiority or equality, people on all sides can feel that their group is not being accorded as much status as it deserves, the feeling of status indignity. Further, political contests can lead people on all sides to feel excluded. We show that status indignity and exclusion are connected and can lead to radicalization. In reviewing research on social dominance orientation, right-wing authoritarianism, and collective narcissism, we identify evidence that regressive radicalization is more likely than progressive radicalization due to the psychological assumptions of people who favor regressive versus progressive movements.

The theoretical models propose that chronic social exclusion inevitably leads individuals into a state of psychological resignation and behavioral withdrawal. After reviewing the literature addressing chronic exclusion among general and marginalized populations, we propose that the chronic exclusion–resignation link might not be inevitable and that chronically excluded individuals remain sensitive to novel social affiliations. From here, we discuss how chronic exclusion and the resignation stage can sensitize individuals to the early stages of the radicalization process. We propose that the indomitable need for affiliation may drive chronically excluded individuals toward social resurrection when supported by prosocial sources of reconnection. However, without such avenues, radicalization may become an appealing path for reaffiliation, leading to extremist groups. This chapter elucidates the complex interplay between chronic exclusion, resignation, and radicalization, and it might inform the development of targeted strategies fostering social reintegration and preventing the allure of extremist ideologies among chronically excluded individuals.

Bayle invites us to reflect on the psychological effects of conformity on the dissenter himself, forced to violate his conscience, as well as the counter-intuitive implications of this infringement. Bayle suggests that infringements on conscience are experienced as deep violations by the dissenter, arguably just as unsettling as more violent forms of discipline and coercion. The experience of conforming to the state religion does not merely corrode mutual understanding among citizens but asks individuals to endure the taxing experience of suppressing and violating their consciences. Hypocritical conformity is not merely a trivial demand with little consequence for their integrity, as advocates of religious persecution insist, but a deeply felt violation that reverberates even long after the act of conformity is finished. Even more discerningly, Bayle recognizes that hypocritical conformity exacerbates conscientious fervor. Hypocritical conformity does not merely fail to inspire genuine conversion; it also radicalizes dissenters and urges them to be even more committed to their conscience. In an attempt to transform dissenters through hypocritical conformity, the state risks emboldening dissenters even further and inciting backlash against the state.

Chapter 9 is dedicated to three processes steering the cyclicity of protest, namely politicization, polarization, and radicalization. Simon and Klandermans elaborated on the dynamics of politicization of collective identity. A process of politicization implies support of third parties is sought and the environment becomes divided into allies and opponents. Polarization concerns distancing of the opposing camps. The more polarized the relationship becomes, the less deviation from the group’s opinions and actions is accepted and the more opposing opinions and acts are rejected. Eventually, this may result in radicalization. Also, in declining movements with many “exiters,” sustained participation can indicate radicalization. Take the violent Black Panthers, which played a short but important part in the civil rights movement, believing that Martin Luther King’s non-violent campaign had failed and any promised changes to their lifestyle via the “traditional” civil rights movement would take too long or simply would not be introduced at all. Hence, in light of the declining civil right movement, both disengagement and radical sustained participation were observed. To understand the social psychological correlates of the volatility of protest, politicization, polarization, and radicalization warrants elaborate investigation.

Using interview data from protesters and frontline police, this chapter examines the transition of protest policing, from soft to hard models, amid the recent unrest in Hong Kong. While police-centric explanations in the protest policing literature view police as intentional decision-makers who can choose from a variety of policing strategies, we employ a mixed-embeddedness framework that reveals a number of factors—external to police—that have deprived the Hong Kong Police Force of its capacity to facilitate peaceful protest through soft strategies of communication and negotiation. These include, (1) a legitimacy crisis of governance in Hong Kong (a macrolevel factor), (2) the erosion of police authority within the local political culture (a mesolevel factor), and (3) stylistic changes in police–protester interactions, involving the increased use of masks and collective action frames of identification as victims of police (microlevel factors). Together, these factors inaugurated reaction spirals that led to the end of soft, facilitative protest-policing in Hong Kong.

Chapter 7 explains how militant Islamist leaders adapted “traditional” Egyptian rural norms in ways that allowed them both to supplant the political power of local notables, while simultaneously institutionalizing extortion practices and implementing their own brand of “law and order.” Islamic militants exploited the high levels of social and economic uncertainty in Cairo’s informal housing areas. An important reason behind the popularity of radical Islamists among local residents is due to the ways in which their leaders have utilized highly coercive methods to settle local disputes and enforce informal labor contracts for their members, while simultaneously preaching against the ills of conspicuous consumption in their sermons and imposing strict Islamic modes of conduct. The chapter shows how the socio-economic conditions that have served, as a “recruiting ground” for Islamist radicals was made possible as result of economic change at both the international as well as domestic level.

This chapter provides a detailed discussion of the main terms used in the books (e.g., radicalization, extremism, milieus, groups, and ideology). The core of the chapter is a review of the state of the art regarding the development and change of political attitudes in general and within extremist environments. The methodology of the book (criminological storyline approach) is explained and the most pressing gaps in the research literature regarding (extremist) side-switching are outlined. In short, the topic is highly under-researched and promises to offer fascinating insights into the relationship between extremists and their groups.

Chapter 7 explains how militant Islamist leaders adapted “traditional” Egyptian rural norms in ways that allowed them both to supplant the political power of local notables, while simultaneously institutionalizing extortion practices and implementing their own brand of “law and order.” Islamic militants exploited the high levels of social and economic uncertainty in Cairo’s informal housing areas. An important reason behind the popularity of radical Islamists among local residents is due to the ways in which their leaders have utilized highly coercive methods to settle local disputes and enforce informal labor contracts for their members, while simultaneously preaching against the ills of conspicuous consumption in their sermons and imposing strict Islamic modes of conduct. The chapter shows how the socio-economic conditions that have served, as a “recruiting ground” for Islamist radicals was made possible as result of economic change at both the international as well as domestic level.

In 1818, the Allied Council had stabilized the Bourbon regime, and implemented principles of demilitarization and de-Bonapartization. However, the implementation of ‘indirect rule’ was met with increasing resistance among the French populace, and the Allies began to doubt whether the occupation of France was contributing to the security of the country, and by extension, of Europe: a worry that reached its culmination when the Duke of Wellington was attacked. Allied policies meant to discourage Bonapartist sympathies and secure Europe seemed to fuel polarization and radicalization in France instead. By exiling and imposing strict disciplinary measures against suspected Bonapartists and radicals, they had inadvertently spread revolutionary sentiment beyond France’s borders, especially to vulnerable neighbour states such as Belgium. The costs of the occupation and the humiliation of the French through reparation measures put a further heavy burden on the political and social peace of post-Napoleonic Europe.