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Radicalization and the internet: 25 years of (online) radicalization research

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Radicalization and the internet: 25 years of (online) radicalization research

Summary

This scoping review synthesizes 25 years (2000–2025) of scholarship on the internet’s role in radicalization, analyzing 382 publications to map conceptual frameworks, methods, and substantive findings. The authors define radicalization as an incremental, multi-factor process culminating in adoption of radical/extremist ideologies and/or acceptance of ideologically motivated violence, and they argue that the internet acts as a catalyst rather than a root cause. Their central conceptual move is to dissolve the online/offline binary in favor of hybrid socio-technical environments, and to organize a fragmented literature through a dual lens combining macro/meso/micro levels with Lasswell’s communication-process elements (communicator, content, medium, recipient). The review documents an “empirical turn” since 2018, growing phenomenological diversification beyond left-right categories, and persistent gaps in longitudinal and causal evidence.

Key Contributions

  • The broadest temporal and cross-phenomenological synthesis of online radicalization research to date (382 publications, 2000–2025).
  • An integrative definition of radicalization stressing processual, multi-factor, multi-outcome dynamics.
  • A dual analytical framework pairing macro/meso/micro levels with Lasswell’s communicator/content/medium/recipient schema to disaggregate “the internet” into analyzable factors.
  • A typology of recurring factor clusters (algorithmic curation, content strategies, communicator tactics, exposure/engagement) linked to radicalization mechanisms.
  • A mapping of geographic, phenomenological, methodological, and platform-coverage biases in the field.
  • Identification of research gaps — longitudinal/causal designs, understudied platforms (Gab, 4chan, BitChute, gaming), and non-Western contexts.

Methods

Scoping literature review of publications from January 2000 through December 2025, searched across Web of Science, Communication and Mass Media Complete, ACM Digital Library, the VOX-Pol library, and Google Scholar using bilingual (English/German) Boolean queries on radicalization/extremism/terrorism and internet/platform terms. Two-stage screening reduced 3,532 records to 382 included items. Coding combined quantitative field descriptives (year, type, geography, phenomenon, method) with conceptual coding of definitions and analytical lenses, plus qualitative extraction of findings and implications. Intracoder reliability on a 10% subsample yielded Krippendorff’s α between 0.90 and 1.00. The analytic framework fuses Lasswell’s communication formula with a macro/meso/micro radicalization perspective.

Findings

  • 76.7% of included works are peer-reviewed journal articles; substantial gray literature reflects the field’s applied orientation.
  • Output grew sharply after 2014, peaking at 47 publications in 2025; 193 of 382 appeared in 2021–2025.
  • Geographic focus is strongly Western (UK, Germany, US); over 50% of studies are not country-specific.
  • Islamist extremism dominates (34%), followed by far-right (20.2%); since 2022 attention to misogynist/Incel, QAnon/conspiracy, and anti-system radicalization has grown.
  • Empirical work (71.7%) dominates after 2018; qualitative methods lead, with computational and mixed-methods rising. Longitudinal studies remain rare (n=34).
  • Less than half (47.4%) explicitly define radicalization; only 15.7% define online radicalization specifically.
  • Macro-level studies (48.2%) emphasize information/contact affordances, algorithmic curation, and mainstreaming of extremist content.
  • Meso-level studies (18.6%) focus on echo chambers, co-radicalization, and emotional convergence within communities.
  • Micro-level studies (30.9%) suggest hybrid and online pathways are increasingly common, especially for socially isolated individuals and “lone wolves”; some evidence points to shortened radicalization timelines.
  • Platform research clusters on Twitter/X (n=36), YouTube (n=22), Facebook (n=21), and increasingly Telegram (n=17); fringe platforms and gaming spaces remain understudied.
  • Short-term exposure rarely produces radicalization on its own; effects are contingent on prior attitudes, identification, social dominance orientation, authoritarianism, trait aggression, and need for significance, with media literacy and democratic trust as protective factors.

Connections

This review provides the broadest conceptual scaffolding for the topic and frames many of the empirical investigations conducted alongside it: Bailard2024-pj speaks to the macro/medium-level questions of algorithmic curation and platform affordances flagged here as central, while Nangle2026-yo and Karo2026-dn engage the phenomenological diversification (misogynist/Manosphere, conspiracy-driven, anti-system currents) that the authors identify as a growing but under-theorized strand. Bouchafra2026-ts is relevant to the recipient/micro-level findings on exposure effects and individual susceptibility factors.

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