Violent extremism and terrorism remain significant priorities on the national and international political agenda. The terrorist attacks in Western Europe and the US, the COVID-19 pandemic, and the current violent conflicts in the Middle East have led to an increase in (violent) radicalization within jihadist, right-wing, and left-wing circles. Additionally, new, more time-bound forms of extremism have emerged. Despite two decades of terrorism research, the field remains characterized by conceptual ambiguity, analytical vagueness, and fragmentation. As a result, key questions remain unanswered, specifically regarding why (causal factors) and how (causal mechanisms) (violent) extremism occurs.

This doctoral research examines why and how the process towards (violent) extremism occurs, starting from an integrated theoretical model. Not only the causal factors underlying (violent) extremism were studied, also the interaction between the different factors over time. A unique aspect of the research is the insider perspective. Specifically, the life stories and experiences of 26 prisoners convicted of right-wing or religious extremism (e.g., Syria fighters) were studied, comprising a total of over 40 informal conversations and 62 in-depth interviews conducted between February 2021 and February 2023. Additionally, an innovative research method, life diagrams, was employed, where respondents outlined their life trajectories on a graph, taking into account spatial and temporal factors.

The research findings reveal that (violent) extremism is a dynamic, non-linear process shaped by the interaction of various internal and external factors over time. Four key elements have been identified: predisposing life experiences, cognitive openings, the violence-legitimizing in-group, and ideology. Consistent with recent empirical research, the study affirms the multifactorial nature of (violent) extremism, thereby challenging deterministic portrayals of it. Respondents describe their extremism journey as complex and dynamic, with occasional abrupt shifts in thinking and behavior. Processes can accelerate, decelerate, or halt, leading individuals to engage, disengage, or even re-engage in (violent) extremism. Furthermore, the research underscores the existence of multiple individual pathways to (violent) extremism. A critical finding is the absence of a causal link between extremist beliefs and violent behavior. Some individuals maintain extremist beliefs for years without resorting to violence, while others exhibit violent behavior without complete ideological indoctrination. In essence, diverse individual trajectories yield different outcomes, with violence being more of an exception than a rule. A crucial takeaway is the challenge of discerning, from an external standpoint, when individuals align with a (violent) extremist ideology and when they will actively endorse violence, given that these processes predominantly occur internally.