Many of you read my Cato blog post from September 11 about the frequency of deadly, politically motivated terrorist attacks in the United States. People are apprehensive about these attacks in the wake of the assassination of Charlie Kirk by a left-wing, politically motivated terrorist. Here’s a short follow-up with my data and a detailed explanation of the methods and sources because linking to my earlier work on similar topics and writing, “I did the same thing,” left several readers confused.
Table 1 lists the killers, the date of their attacks or the closest relevant date known (such as a court appearance), the number of fatalities, the visa they entered the US on if they were foreign-born, their countries of birth, and their motivating ideologies. Please let me know if you see any errors or omissions by emailing me here, leaving a comment below, or yelling at me on X.
The methodology and sources sections below are almost identical to my earlier papers on terrorism, but I rewrote them so they are easily accessible.
Methodology
My research uses an expansive definition of terrorism, which is the threatened or actual use of illegal force and violence by a nonstate actor to attain a political, economic, religious, or social goal through coercion, fear, or intimidation. This analysis examines terrorism from January 1, 1975, to September 10, 2025. It focuses on politically motivated terrorists who have murdered at least one person in their attacks.
For attacks that included many terrorists, the number of victims is divided equally among the terrorists in each attack. For instance, the 1993 World Trade Center attack was committed by six foreign-born terrorists who murdered six people, so each terrorist is credited with one death. Those innocent people killed or injured by the police or security forces responding directly to an attack are counted as victims of the terrorist attacks.
The ideologies of foreign-born terrorists are divided into the following categories: Islamism, foreign nationalism, right (incel ideology, anti-abortion, white supremacist, etc.), left (communism, animal rights, environmentalism, anti-white, etc.), separatism of various kinds, and unknown/other. The citizenship of terrorists is their country of origin at birth.
The most difficult challenge was distinguishing terrorism from so-called hate crimes, where the offender commits a violent or property crime against an individual or small group that is motivated by ethnic, racial, national, religious, or other forms of bigotry based on his personal opinions, but with no broader political, economic, religious, or social goal. Terrorism, to repeat, is often motivated by personal hatred, but the attacker must be aiming at a broader political, economic, religious, or social goal to be terrorism. As with most crimes, the perpetrator’s intent is paramount in identifying the crime.
Lastly, this analysis focuses on deaths for several reasons. First, deaths are all the same amount of harm for analysis. Second, other measures like injuries, incidents, or arrests are all very different. Injuries can range from a scratch to an amputated limb, but they are counted the same. It’s also inappropriate to count incidents as all the same because throwing a sandwich and murdering somebody are almost incomparable levels of harm. Any analysis that counts covering somebody in lettuce as the same as killing them is unserious. Similarly, poll results about the acceptability of political violence have never impressed me for many good reasons that should make you doubt survey results.
Sources
The identities of the politically motivated terrorists come from 18 main datasets and documents. The first is Terrorism Since 9/11: The American Cases, edited by John Mueller. The second source is the Fordham University Center on National Security’s terrorism trial report cards, a compilation of all the trials for terrorism cases for Islamic State of Iraq and Syria (ISIS) members in the United States, as well as statistical analyses and overviews. Third is the Congressional Research Service. The fourth source is the RAND Corporation. The fifth source is the Global Terrorism Database (GTD) maintained by the National Consortium for the Study of Terrorism and Responses to Terrorism at the University of Maryland, College Park. Sixth are the results of numerous Freedom of Information Act requests by various organizations and individuals asking for all terrorism-related convictions since 9/11. Sources seven through 19 are the New America Foundation; The Intercept; the Investigative Project on Terrorism; the research of University of North Carolina sociology professor Charles Kurzman; the George Washington University Program on Extremism; the Center for Immigration Studies; the Southern Poverty Law Center; research by the National White Collar Crime Center; the Terrorism Research Center at the Fulbright College of Arts and Sciences at the University of Arkansas; a dissertation by Catlyn Kenna Keenan; numerous FBI reports on terrorist incidents in the United States; press releases, statements, or speeches issued by the Department of Justice; the Center for Strategic and International Studies (full data access here has not yet been granted); and every news source you can imagine.
Individual information for the politically motivated killers, their ideologies, their countries of origin, visas, the number of people murdered, and other information comes from the sources mentioned above, as well as news stories, court documents, and other government reports. Many of the foreign-born killers entered the United States on one visa but committed their attacks after they switched to another visa, were naturalized, or lost immigration status. This report classifies those foreign-born terrorists under the visa they had when they initially entered the country. The only exception is for asylum seekers, who are counted under the asylum visa category.