terrorism
Definition
Terrorism is a form of asymmetric intergroup conflict, commonly described as the warfare of the weak, in which non-state actors use or threaten force to further political, social, or ideological ends. The longstanding definition treats ideological motivation as a defining characteristic, yet a growing number of lone-actor perpetrators, overwhelmingly young men, commit mass violence with no clear or consistent ideology, which places pressure on that assumption. Official classification systems reflect this tension: the FBI and DHS distinguish between ethnically motivated, anti-government, environmental, abortion-related, and all-other domestic terrorism threats, with the last category substituting reference to social agendas for any requirement of ideological coherence. Some individuals charged with terrorism offences, such as those prosecuted under nihilistic violent extremism frameworks, valorise violence as intrinsically good rather than as a means to any political end, and neither police nor inquiry panels have found evidence of political, religious, or racial ideological cause in their cases. Conceptual debate in the field has consequently focused on whether hybrid, mixed, or ideologically incoherent perpetrators constitute a genuinely new phenomenon or a measurement artefact, with UK Prevent data showing the no-ideology referral category reaching nearly 5,000 cases by March 2025, far exceeding referrals for Islamist or extreme right-wing ideologies.
Sources: McCauley (2026), Cassam (2026), Baele (2026)
Related Terms
- ideology (3 shared articles)
- salad bar (2 shared articles)
- extremism (2 shared articles)
- violence (2 shared articles)
- political violence (1 shared article)
- online extremism (1 shared article)
- salad bar extremism (1 shared article)
- composite extremisms (1 shared article)
- fixation (1 shared article)
- violent extremism (1 shared article)
- mobilization frame (1 shared article)
- nihilistic violent extremism (1 shared article)
- group conflict (1 shared article)
Applications
Terrorism and Ideology
The relationship between terrorism and ideology is contested. Ideology has historically been treated as a defining characteristic of terrorism, yet the degree to which any individual perpetrator must be ideologically motivated for their violence to qualify as terrorism remains unresolved, and for some actors ideological commitment may be entirely absent or merely a byproduct of social engagement with fellow travellers. Efforts to classify offenders who blend, migrate between, or lack coherent ideologies have produced competing typologies, and practitioners in both the United States and the United Kingdom report that ideologically indeterminate cases now represent the largest and fastest-growing share of referrals and prosecutions.
Sources: Cassam (2026), Baele (2026), Horgan & Shayler (2026)
Terrorism and Radicalization
Radicalization research has long assumed that the role of ideas in the pathway to terrorism can be traced through ideological content, but this assumption is challenged by lone-actor cases in which primary attraction to violence precedes any ideological framing. Conceptual debate has produced competing proposals for how to account for perpetrators who lack formal ties to designated extremist organisations or who blend and migrate between ideological positions. One proposed alternative to ideology-centred accounts frames the role of ideas through collective action framing, distinguishing diagnostic, prognostic, and motivational dimensions that apply to both perpetrators and targets across all official categories of violent extremism.
Sources: Cassam (2026), Baele (2026), Horgan & Shayler (2026), McCauley (2026)
Terrorism and Violent Extremism
Terrorism and violent extremism are closely related but not coextensive categories. Under US government definitions, violent extremism encompasses individuals who further political or social goals through unlawful force, and this framing is broad enough to include actors who lack a single coherent ideology, whereas terrorism has traditionally required ideological motivation as a threshold condition. Cases such as that of Axel Rudakubana illustrate the gap between the two categories: he was treated as a violent extremist despite the absence of any detectable political, religious, or racial ideological cause, demonstrating that an individual can be classified as an extremist under one framework while falling outside the standard definition of a terrorist under another.
Sources: McCauley (2026), Cassam (2026)
