Which non-Islamist extremist groups carried out the most lethal attacks since 2000?
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Executive summary
Since 2000, the deadliest non‑Islamist extremist violence has come from three broad categories: far‑right/white‑supremacist movements (notably in the United States and Europe), ethno‑nationalist and separatist insurgencies (for example the LTTE in Sri Lanka), and a much smaller number of far‑left or single‑issue attackers; however, globally Islamist groups still account for the majority of terrorist victims, so non‑Islamist groups dominate lethality in some places and time periods but not worldwide [1] [2] [3] [4].
1. Key sources and what they can and cannot show
Judgements about “most lethal” depend on datasets and definitions: the Global Terrorism Database compiles event‑level data worldwide and is commonly used for comparative work [5] [6], while national assessments and syntheses (DHS/Homeland Threat Assessment summaries cited in public reporting and academic reviews) highlight regional shifts such as the rise in white‑supremacist lethal attacks in the United States in recent years [1] [7]. These sources together allow comparison by actor type, but no single provided source gives a complete, globally ranked list of non‑Islamist groups by death toll since 2000, so the analysis must triangulate patterns across datasets [5] [6].
2. The rise in lethality from far‑right and white‑supremacist extremists
In the United States and parts of Europe, white‑supremacist and other right‑wing extremists have been responsible for a disproportionate share of lethal domestic attacks in recent years: U.S. federal reporting and syntheses note that white supremacist extremists conducted half of lethal domestic attacks in a 2018–2019 window and were responsible for the majority of deaths in that sample [1], while academic centers tracking U.S. incidents report a sharp increase in the proportion and lethality of right‑wing incidents across the 2010s [7]. European cases such as the Anders Breivik massacre in Norway underscore that single far‑right actors can produce exceptionally deadly events even if organizational footprints are diffuse [8].
3. Ethno‑nationalist/separatist insurgencies remain highly lethal in specific theatres
Outside the “right/left” framework, ethno‑nationalist and separatist movements have produced major death tolls since 2000: Sri Lanka’s Liberation Tigers of Tamil Eelam (LTTE) conducted high‑casualty suicide and ambush attacks into the 2000s and are recorded in national counterterror timelines as inflicting large numbers of fatalities [2]. Databases like the GTD capture these insurgent events alongside ideological terrorism, meaning separatist campaigns and insurgencies can dominate national death totals even when they are not classified as “far‑right” or “far‑left” [5] [6].
4. Far‑left, single‑issue, and other non‑Islamist actors: frequent but less fatal
Far‑left and environmental extremist attacks increased in some early‑2000s windows but tended to be far less lethal; for example, START analysis shows a rise in the number of left‑wing attacks in the 2000s in the U.S. without corresponding lethality, while “single‑issue” actors appear frequently in profile counts but with lower death totals [7] [1]. This pattern—many incidents but relatively few fatalities—contrasts with the smaller set of high‑fatality operations carried out by some right‑wing and separatist actors [7] [1].
5. Context: Islamist groups still account for the lion’s share of global terrorism deaths
Any assessment of non‑Islamist lethality must be placed against the dominant global pattern: multiple analyses and compilations show that a handful of Islamist extremist organizations (ISIS, al‑Qaeda, Boko Haram, al‑Shabaab, the Taliban) produced the majority of global terrorism deaths across the 2000–2024 period, meaning non‑Islamist groups, even when locally lethal, do not collectively exceed those Islamist groups in global victim counts [3] [4] [9].
6. Conclusion—who carried out the most lethal non‑Islamist attacks since 2000?
Measured regionally and by event, the most lethal non‑Islamist attacks since 2000 have mainly been the product of far‑right/white‑supremacist actors in the U.S. and Europe and of ethno‑nationalist/separatist insurgencies such as the LTTE in their theatres of operation; far‑left and single‑issue actors produced more incidents but far fewer deaths [1] [7] [2]. Globally, however, Islamist extremist groups account for the majority of victims, so non‑Islamist actors are often the deadliest within certain countries or periods but not the leading cause of terrorism fatalities worldwide over the same span [3] [4].