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Fact check: Which extremist groups have been responsible for the most fatalities in the US since 2010?
Executive Summary
Since 2010, multiple datasets show right-wing extremists account for the plurality of U.S. domestic terrorism fatalities across much of the last decade, but scholars and databases diverge on recent trends and on whether left-wing violence has risen to parity. Key quantitative snapshots attribute most deaths to racially or ethnically motivated and right-wing actors, while newer analyses note a post-2016 uptick in left-wing incidents — creating conflicting portraits depending on the timeframe and definitions used [1] [2] [3] [4].
1. Who the numbers point to when you look at fatalities
The most consistent finding across the provided sources is that right-wing and racially/ethnically motivated extremists have been responsible for the largest share of fatalities in the period referenced by several datasets. A Center for Strategic and International Studies summary reports 112 fatalities from right-wing attacks versus 13 from left-wing attacks over its examined period and notes a much higher annual frequency of right-wing incidents [1]. The Government Accountability Office similarly identifies racially or ethnically motivated violence as the most lethal domestic terrorism category between 2010 and 2021, with anti-government or anti-authority actors second [3]. These agency and think‑tank snapshots converge on the point that lethality clusters with ideologies linked to racial animus and far‑right motivations [1] [3].
2. The rising-left-wing narrative complicates the simple picture
Some analysts emphasize a changing balance: researchers at the Program on Extremism and related briefings indicate left-wing attacks have increased since about 2016 and that 2025 marked a year when left-wing incidents outnumbered far-right incidents in some trackers [4]. The TEVUS database and GW Extremism Tracker provide comprehensive incident-level data that can show shifting frequencies, but multiple teams warn that an increase in incident counts does not necessarily translate to a higher fatality toll, because many left-wing incidents are less lethal on average compared with the deadliest right-wing attacks [5] [6] [4]. The contrast between frequency and lethality is central: more events does not equal more deaths, and datasets differ on which metric they emphasize [5] [4].
3. Government reporting, definitions, and timeframe choices drive different conclusions
Official FBI and DHS assessments and the GAO use curated definitions that shape which incidents are counted as domestic terrorism, with the FBI/DHS strategic reports providing incident descriptions and investigative outcomes for 2015–2019 and beyond [7] [8]. The GAO’s 2010–2021 window finds 231 domestic terrorism incidents and highlights racially motivated attacks as the most lethal [3]. Analysts point out that choosing different start/end dates, including or excluding certain ideologies, and relying on fatality counts versus incident counts lead to divergent headlines — for example, a decade‑wide fatality tally favors right‑wing culpability, while recent year‑to‑year incident tracking can show a rise in left‑wing activity [1] [2] [3].
4. Data limitations and methodological differences you need to know
All referenced sources caution that comparisons are sensitive to methodology: databases vary in event inclusion, coding rules, and whether they count only perpetrator or also collateral fatalities. Statista’s compilation highlights historical outliers like the Oklahoma City and Pulse attacks to show how single events can dominate tallies, underscoring how one mass‑casualty incident can skew “most fatal” labels [9]. The TEVUS and GW trackers aim for comprehensive catalogs but note the challenges of classification and reporting lags [5] [6]. Therefore, claims such as “which group caused the most fatalities” require explicit statements about which dataset, period, and fatality definition are being used [9] [5].
5. Bottom line: what the evidence actually supports and what remains unsettled
The weight of the compiled, multi‑year fatality data identifies right‑wing and racially/ethnically motivated extremists as responsible for the most deaths in the U.S. since 2010, particularly when measured by fatalities rather than incident counts [1] [3]. However, recent analytic updates and incident trackers show an increase in left‑wing incidents since 2016, creating a contested picture about contemporary trends and signaling the need to distinguish between frequency and lethality [4] [2]. Researchers and policymakers should therefore cite the exact dataset and timeframe when making claims, because different choices yield different, defensible conclusions [8] [5].