terrorism
Definition
Terrorism is a form of politically motivated violence in which perpetrators may draw on ideological content to legitimize their actions, seek notoriety, or justify grievances, without necessarily holding deep or coherent commitment to any single belief system. Contemporary perpetrators increasingly appear to mix, hop between, or selectively appropriate elements from multiple and sometimes contradictory ideologies, a pattern that complicates classification and response efforts. The degree of intentionality involved in such ideological mixing remains contested, and it is unclear whether the resulting belief combinations reflect genuine ideological fusion or more superficial, instrumental affiliation. Young people are disproportionately represented among those radicalized in recent years, and U.S. START data recorded a 311% increase over the past decade in youth radicalized without formal ties to designated extremist organizations.
Sources: Horgan & Shayler (2026)
Applications
Terrorism and Ideological Extremism
Terrorism and ideological extremism are related but distinct phenomena. Not every extremist is a terrorist, and some terrorist actors display belief systems too incoherent or idiosyncratic to map onto established extremist categories. The National Counter Terrorism Center, DHS, and FBI distinguished in 2023 between offenders who mix ideologies and those who hop between them, a distinction that matters for how practitioners classify cases and design interventions. Toronto's ETA program classified fewer than 5% of clients as 'Mixed Issue,' suggesting that rising case counts may partly reflect shifts in practitioner classification practices rather than a genuine surge in ideologically mixed terrorism.
Sources: Horgan & Shayler (2026)
Terrorism and Radicalization
Radicalization into terrorism increasingly occurs outside formal organizational structures, with online ecosystems and conspiracy content contributing to violent extremist mobilization. The diminishing influence of strict hierarchical organizations means that many individuals radicalize without any formal ties to designated groups, a trend documented in U.S. START data showing a marked increase in such cases among youth over the past decade.
Sources: Horgan & Shayler (2026)
