Fact check: Which right-wing extremist groups have been responsible for the most attacks in the US since 2015?

1. Why the question is harder than it looks: groups, lone actors and messy data

The primary analytic challenge is that the sources show different units of analysis: some count fatalities, others count incidents, and many attacks are perpetrated by unaffiliated or lone actors rather than identifiable formal groups. The summaries indicate that researchers attribute most lethal domestic terrorism to right-wing ideologies overall, yet the datasets differ on whether to credit structured organizations versus decentralized networks or individuals acting on shared extremist beliefs ^{[1] [2]}. The GW Extremism Tracker explicitly documents monthly incidents and court actions without producing a neat ranked list of groups, underscoring how public trackers prioritize event narratives over aggregated group tallies ^[3].

2. What the sources claim about frequency and lethality of right-wing violence

Multiple analyses assert that right-wing extremist violence has been both more frequent and more deadly than left-wing violence in the United States across recent years, with one study citing roughly 75–80% of domestic terrorism deaths since 2001 as stemming from right-wing actors ^[1]. Another 2025 evaluation highlighted a sharp fall in right-wing incidents during 2025 but maintained that right-wing attacks produced far more fatalities over the prior decade—112 versus 13—showing persistence in lethality even if annual incident totals fluctuate ^[2].

3. Where the evidence stops short on naming the “most responsible” groups

The supplied materials repeatedly stop short of a definitive list of named groups responsible for the most attacks since 2015. The nation-level analyses emphasize notable attacks—such as Charleston and Pittsburgh—as emblematic of right-wing lethality, but they do not tie a majority of incidents to a small number of formal organizations; rather, they implicate ideologies, networks, and individuals inspired by extremist movements ^{[1] [3]}. This gap suggests that counting attacks by group requires a different methodology and dataset than the ones summarized here.

4. The role of lone-actor and decentralized movements in right-wing violence

The summaries imply a large role for lone actors and decentralized movements in right-wing terrorism, which complicates attribution to named groups. High-profile mass-casualty events often involve individuals motivated by extremist ideologies—white supremacy, anti-government beliefs—without formal operational ties to established organizations, meaning that aggregate death totals reflect ideological currents more than group command structures ^[1]. The GW Tracker’s approach of cataloging incidents and court filings reflects the reality that many prosecutions and investigations focus on individuals or small cells rather than multi-attack organizations ^[3].

5. Divergent interpretations and potential agendas in recent analyses

The materials show interpretive divergence: one September 2025 study emphasizes a 2025 drop in right-wing attacks and a rise in left-wing incidents, framing a short-term shift in patterns, while others underscore the long-term predominance of right-wing lethality ^{[2] [1]}. These contrasting emphases can reflect differing research windows, definitions of “attack,” or editorial framing, and they may serve distinct agendas—some highlight improving trends to argue for reduced threat level, others stress persistent asymmetry to prioritize counter-extremism resources ^{[2] [1]}.

6. What the evidence would need to answer the original question directly

To produce a ranked list of specific right-wing groups responsible for the most attacks since 2015 requires granular incident-level coding linking perpetrators to formal organizations, consistent definitions of “attack,” and an explicit decision rule for attributing credit when perpetrators claim inspiration but no organizational tie. The GW Extremism Tracker demonstrates the necessary raw documentation exists at the incident level, but the present syntheses do not perform or present that attributional aggregation ^[3]. Without such a dataset in the supplied materials, any group ranking would be speculative.

7. Bottom line and recommended next steps for a definitive answer

The supplied analyses establish that right-wing extremism has caused the majority of domestic terrorism fatalities and that patterns shifted in 2025, but they do not identify which named right-wing organizations carried out the most attacks since 2015 ^{[1] [2] [3]}. A definitive answer requires incident-by-incident coding from comprehensive trackers and law-enforcement or academic datasets that explicitly attribute attacks to groups; the GW Tracker is a logical primary source for such work, but further aggregation and transparent methodology are necessary before producing a ranked list ^[3].