The Escalating Terrorism Problem in the United States

CSIS Briefs


The United States faces a growing terrorism problem that will likely worsen over the next year. Based on a CSIS data set of terrorist incidents, the most significant threat likely comes from white supremacists, though anarchists and religious extremists inspired by the Islamic State and al-Qaeda could present a potential threat as well. Over the rest of 2020, the terrorist threat in the United States will likely rise based on several factors, including the November 2020 presidential election.

On June 3, 2020, federal authorities arrested three individuals allegedly associated with the “boogaloo” movement, a loosely-organized group of extremists preparing for a civil war, for conspiring to cause violence in Las Vegas and possessing an improvised incendiary device.1 Less than a week later, law enforcement officials near Richmond, VA, arrested Harry H. Rogers, a member of the Ku Klux Klan, for driving a vehicle into peaceful protesters. Around the same time, members of a Brooklyn anarchist group urged its supporters to conduct “rebellion” against the government.2 Extremists from all sides flooded social media with disinformation, conspiracy theories, and incitements to violence in response to the protests following the death of George Floyd, swamping Twitter, YouTube, Facebook, and other platforms.3

This CSIS brief examines the state of terrorism in the United States. It asks two sets of questions. First, what are the most significant types of terrorism in the United States, and how has the terrorism threat in the U.S. homeland evolved over time? Second, what are the implications for terrorism over the next year? To answer these questions, this analysis compiles and analyzes an original data set of 893 terrorist plots and attacks in the United States between January 1994 and May 2020.

This analysis makes several arguments. First, far-right terrorism has significantly outpaced terrorism from other types of perpetrators, including from far-left networks and individuals inspired by the Islamic State and al-Qaeda. Right-wing attacks and plots account for the majority of all terrorist incidents in the United States since 1994, and the total number of right-wing attacks and plots has grown significantly during the past six years. Right-wing extremists perpetrated two thirds of the attacks and plots in the United States in 2019 and over 90 percent between January 1 and May 8, 2020. Second, terrorism in the United States will likely increase over the next year in response to several factors. One of the most concerning is the 2020 U.S. presidential election, before and after which extremists may resort to violence, depending on the outcome of the election. Far-right and far-left networks have used violence against each other at protests, raising the possibility of escalating violence during the election period.

The rest of this brief is divided into the following sections. The first defines terrorism and its main types. The second section analyzes terrorism trends in the United States since 1994. The third examines far-right, far-left, and religious networks. The fourth section highlights the terrorism threat over the next year.


This analysis focuses on terrorism: the deliberate use—or threat—of violence by non-state actors in order to achieve political goals and create a broad psychological impact.4 Violence—and the threat of violence—are important components of terrorism. Overall, this analysis divides terrorism into four broad categories: right-wing, left-wing, religious, and ethnonationalist.5 To be clear, terms like right-wing and left-wing terrorism do not—in any way—correspond to mainstream political parties in the United States, such as the Republican and Democratic parties, which eschew terrorism. Instead, terrorism is orchestrated by a small minority of extremists.

First, right-wing terrorism refers to the use or threat of violence by sub-national or non-state entities whose goals may include racial or ethnic supremacy; opposition to government authority; anger at women, including from the incel (“involuntary celibate”) movement; and outrage against certain policies, such as abortion.6 This analysis uses the term “right-wing terrorism” rather than “racially- and ethnically-motivated violent extremism,” or REMVE, which is used by some in the U.S. government.7 Second, left-wing terrorism involves the use or threat of violence by sub-national or non-state entities that oppose capitalism, imperialism, and colonialism; pursue environmental or animal rights issues; espouse pro-communist or pro-socialist beliefs; or support a decentralized social and political system such as anarchism. Third, religious terrorism includes violence in support of a faith-based belief system, such as Islam, Judaism, Christianity, and Hinduism, among many others. As highlighted in the next section, the primary threat from religious terrorists comes from Salafi-jihadists inspired by the Islamic State and al-Qaeda. Fourth, ethnonationalist terrorism refers to violence in support of ethnic or nationalist goals—often struggles of self-determination and separatism along ethnic or nationalist lines.

In examining terrorism, this analysis does not specifically address several related phenomena. For example, it does not focus on hate crimes. There is overlap between terrorism and hate crimes, since some hate crimes include the use or threat of violence.8 But hate crimes can also include non-violent incidents such as graffiti and verbal abuse. Hate crimes are obviously concerning and a threat to society, but this analysis concentrates only on terrorism and the use—or threat—of violence to achieve political objectives.


To evaluate the threat posed by terrorism, we compiled a data set of 893 incidents that occurred in the United States between January 1994 and May 8, 2020.9 (The link to the methodology can be found at the end of the brief.) These incidents included both attacks and foiled plots. We coded the ideology of the perpetrators into one of five categories: ethnonationalist, left-wing, religious, right-wing, and other (which included motivations that did not fit into any of the categories). All of the religious attacks and plots in the CSIS data set were committed by terrorists who ascribed to a Salafi-jihadist ideology.

This section analyzes the data in two parts: terrorist incidents and fatalities. The data show three notable trends. First, right-wing attacks and plots accounted for the majority of all terrorist incidents in the United States since 1994. In particular, they made up a large percentage of incidents in the 1990s and 2010s. Second, the total number of right-wing attacks and plots has grown substantially during the past six years. In 2019, for example, right-wing extremists perpetrated nearly two-thirds of the terrorist attacks and plots in the United States, and they committed over 90 percent of the attacks and plots between January 1 and May 8, 2020. Third, although religious extremists were responsible for the most fatalities because of the 9/11 attacks, right-wing perpetrators were responsible for more than half of all annual fatalities in 14 of the 21 years during which fatal attacks occurred.


Between 1994 and 2020, there were 893 terrorist attacks and plots in the United States. Overall, right-wing terrorists perpetrated the majority—57 percent—of all attacks and plots during this period, compared to 25 percent committed by left-wing terrorists, 15 percent by religious terrorists, 3 percent by ethnonationalists, and 0.7 percent by terrorists with other motives.

Figure 1 shows the proportion of attacks and plots attributed to the perpetrator ideologies each year during this period. Right-wing attacks and plots were predominant from 1994 to 1999 and accounted for more than half of all incidents in 2008 as well as every year since 2011, with the exception of 2013. Most right-wing attacks in the 1990s targeted abortion clinics, while most right-wing attacks since 2014 focused on individuals (often targeted because of religion, race, or ethnicity) and religious institutions. Facilities and individuals related to the government and police have also been consistent right-wing targets throughout the period, particularly for attacks by militia and sovereign citizen groups.
The decrease in right-wing activity in the early-2000s coincided with an increase in left-wing activity from 2000 to 2005. Most of these left-wing attacks targeted property associated with animal research, farming, or construction and were claimed by the Animal Liberation Front or the Earth Liberation Front.

As shown in Figure 2, data on the number of terrorist attacks and plots by perpetrator orientation indicate that right-wing terrorism not only accounts for the majority of incidents but has also grown in quantity over the past six years. This increase is reminiscent of the wave of right-wing activity in the 1990s that peaked with 43 right-wing incidents in 1995. The Oklahoma City bombing, which occurred on April 19, 1995, was the second-most deadly terrorist attack in U.S. history, after September 11, 2001. In three recent years—2016, 2017, and 2019—the number of right-wing terrorist events matched or exceeded the number in 1995, including a recent high of 53 right-wing terrorist incidents in 2017. Despite a moderate decrease in 2018 to 29 incidents, right-wing activity again increased in 2019 to 44 incidents. Religious attacks and plots have also shown some increases during this period—notably in 2015, 2017, and 2019—but at a significantly smaller magnitude than right-wing events.



In analyzing fatalities from terrorist attacks, religious terrorism has killed the largest number of individuals—3,086 people—primarily due to the attacks on September 11, 2001, which caused 2,977 deaths.10 The magnitude of this death toll fundamentally shaped U.S. counterterrorism policy over the past two decades. In comparison, right-wing terrorist attacks caused 335 deaths, left-wing attacks caused 22 deaths, and ethnonationalist terrorists caused 5 deaths.

To evaluate the ongoing threat from different types of terrorists, however, it is useful to consider the proportion of fatalities attributed to each type of perpetrator annually. In 14 of the 21 years between 1994 and 2019 in which fatal terrorist attacks occurred, the majority of deaths resulted from right-wing attacks. In eight of these years, right-wing attackers caused all of the fatalities, and in three more—including 2018 and 2019—they were responsible for more than 90 percent of annual fatalities.11 Therefore, while religious terrorists caused the largest number of total fatalities, right-wing attackers were most likely to cause more deaths in a given year.


This section outlines the threat from right-wing, left-wing, and religious networks. In particular, it focuses on the threat from right-wing extremists because of the high number of incidents and fatalities they perpetrated, as highlighted in the previous section. It does not cover ethnonationalist networks, which are not a major threat in the United States today.


There are three broad types of right-wing terrorist individuals and networks in the United States: white supremacists, anti-government extremists, and incels. There are numerous differences between (and even within) these types, such as ideology, capabilities, tactics, and level of threat. Adherents also tend to blend elements from each category. But there are some commonalities.

First, terrorists in all of these categories operate under a decentralized model. The threats from these networks comes from individuals, not groups.12 For example, anti-government activist and white supremacist Louis Beam advocated for an organizational structure that he termed “leaderless resistance” to target the U.S. government.13

Second, these networks operate and organize to a great extent online, challenging law enforcement efforts to identify potential attackers.14 Right-wing terrorists have used various combinations of Facebook, Twitter, YouTube, Gab, Reddit, 4Chan, 8kun (formerly 8Chan), Endchan, Telegram, Vkontakte, MeWe, Discord, Wire, Twitch, and other online communication platforms. Internet and social media sites continue to host right-wing extremist ideas such as the Fourteen Words (also referred to as the 14 or 14/88) coined by white supremacist David Lane, a founding member of the group the Order. The Fourteen Words includes variations like: “We must secure the existence of our people and a future for white children.”15 Far-right perpetrators also use computer games and forums to recruit.16

Third, right-wing extremists have adopted some foreign terrorist organization tactics, though al-Qaeda and other groups have also adopted tactics developed by right-wing movements.17 In a June 2019 online post, a member of the Atomwaffen Division (AWD) stated, “the culture of martyrdom and insurgency within groups like the Taliban and ISIS is something to admire and reproduce in the neo-Nazi terror movement.”18 Similarly, the Base—a loosely organized neo-Nazi accelerationist movement which shares the English-language name for al-Qaeda—uses a vetting process to screen potential recruits, similar to the methods of al-Qaeda.19

This rise in right-wing activity is of national concern; it is not isolated to one region and affects cities of varying sizes. Figure 3 shows the locations of right-wing terror attacks and plots in the United States over the past six years. These incidents occurred in 42 states, Washington, DC, and Puerto Rico.

White Supremacists: White supremacist networks are highly decentralized. Most believe that whites have their own culture that is superior to other cultures, are genetically superior to other peoples, and should exert dominance over others. Many white supremacists also adhere, in varying degrees, to the Great Replacement conspiracy. The conspiracy claims that whites are being eradicated by ethnic and racial minorities—including Jews and immigrants.20 Brenton Tarrant, the Christchurch shooter in New Zealand, and Patrick Crusius, the El Paso Walmart shooter, espoused the most radical view of the Great Replacement conspiracy, known as Accelerationism. As advocated by Tarrant and Crusius, violent accelerationists claim that the demise of Western governments should be accelerated to create radical social change and establish a whites-only ethnostate.21

White supremacists draw inspiration from individuals abroad and at home. Tarrant, for example, drew inspiration from Anders Breivik, who conducted the 2011 terrorist attack in Norway that killed 77 people, and Dylan Roof, who was responsible for the 2015 Charleston Church shooting that killed 9 people in South Carolina.22 Tarrant’s Christchurch attack then inspired terrorist attacks in the United States by John Earnest in California and Patrick Crusius in Texas.23 White supremacist actors have also travelled abroad seeking paramilitary training and networking opportunities. In Spring 2018, for example, members of the Rise Above Movement (RAM) travelled to Ukraine to celebrate Hitler’s birthday and train with the Azov Battalion, a paramilitary unit of the Ukrainian National Guard, which the FBI says is associated with neo-Nazi ideology.24

White supremacist neo-Nazi organizations, such as the Nationalist Socialist Movement, American Nazi Party, Vanguard America, and others often adhere to the Zionist Occupied Government (ZOG) conspiracy theory—that Jews secretly control the U.S. government, the media, banks, and the United Nations. Of particular concern is the emergence of the Atomwaffen Division (AWD), a U.S.-based neo-Nazi hate group with branches in the United Kingdom, Germany, and the Baltics.25 In January 2018, Brandon Russell, founder of the AWD was arrested and sentenced for possessing a destructive device and explosive material.26 Despite similar arrests, the AWD continues to plot, conduct attacks, and recruit. In February, four AWD members—including Cameron Shea, a high-level member and recruiter of the AWD—were arrested for conspiring to targets journalists and activists. They used encrypted chat platforms, distributed threatening posters, and wore disguises.27 Other arrests have been made under non-terrorism-related charges.28

The AWD continues to train and arm their members similar to international terrorist organizations. In January 2018, the AWD hosted a “Death Valley Hate Camp” in Las Vegas, Nevada, where members trained in hand-to-hand combat, firearms, and the creation of neo-Nazi propaganda videos and pictures. In August 2019, leadership members of the AWD attended a “Nuclear Congress” in Las Vegas, Nevada.29 Other white supremacist movements include the Base, the Patriot Front, and the Rise Above Movement.30

Anti-government Extremists: The right-wing terrorist threat also includes anti-government extremists, including militias and the sovereign citizen movement. Most militia extremists view the U.S. government as corrupt and a threat to freedom and rights.31 Other far-right anti-government groups mobilized to protect a perceived threat to individual gun ownership rights. Modern militias are organized as paramilitaries that conduct weapons training and other field exercises.32 The Three Percenters are a far-right paramilitary group that advocates gun rights and seeks to limit U.S. government authorities. In August 2017, Jerry Varnell, a 23-year-old who identified as holding the “III% ideology” and wanted to “start the next revolution” attempted to detonate a bomb outside of an Oklahoma bank, similar to the 1995 Oklahoma City bombing.33 Also, in January 2017, Marq Perez, who discussed the attack in Three Percenter channels on Facebook, burglarized and burned down a mosque in Texas.34

Anti-government extremists, which sometimes blend with white supremacist movements, have used the slang word “boogaloo” as a shorthand for a coming civil war. Several popular Facebook groups and Instagram pages, such as Thicc Boog Line, P A T R I O T Wave, and Boogaloo Nation, have emerged spreading the boogaloo conspiracy. Police in Texas arrested 36-year-old Aaron Swenson in April after he attempted to livestream his search for a police officer that he could ambush and execute.35 Prior to his arrest, Swenson had shared memes extensively from boogaloo pages.

Incels: Involuntary celibates, or incels, conduct acts of violence against women. The incel movement is composed of a loosely organized virtual community of young males. Incels believe that one’s place in society is determined by physical characteristics and that women are responsible for this hierarchy. Incels identify with the writings of Elliot Rodger, who published a 133-page manifesto, titled “My Twisted World.”36 In October 2015, Christopher Harper-Mercer, inspired by Rodger, killed nine people at a community college in Oregon.37 In November 2018, 40-year-old Scott Beierle killed two women in a yoga studio in Tallahassee, Florida, before committing suicide.38


The far-left includes a decentralized mix of actors. Anarchists are fundamentally opposed to a centralized government and capitalism, and they have organized plots and attacks against government, capitalist, and globalization targets.39 Environmental and animal rights groups, such as the Earth Liberation Front and Animal Liberation Front, have conducted small-scale attacks against businesses they perceive as exploiting the environment.40

In addition, the far-left includes Antifa, which is a contraction of the phrase “anti-fascist.” It refers to a decentralized network of far-left militants that oppose what they believe are fascist, racist, or otherwise right-wing extremists. While some consider Antifa a sub-set of anarchists, adherents frequently blend anarchist and communist views. One of the most common symbols used by Antifa combines the red flag of the 1917 Russian Revolution and the black flag of nineteenth-century anarchists. Antifa groups frequently conduct counter- protests to disrupt far-right gatherings and rallies. They often organize in black blocs (ad hoc gatherings of individuals that wear black clothing, ski masks, scarves, sunglasses, and other material to conceal their faces), use improvised explosive devices and other homemade weapons, and resort to vandalism. In addition, Antifa members organize their activities through social media, encrypted peer-to-peer networks, and encrypted messaging services such as Signal.

Antifa groups have been increasingly active in protests and rallies over the past few years, especially ones that include far-right participants.41 In June 2016, for example, Antifa and other protestors confronted a neo-Nazi rally in Sacramento, CA, where at least five people were stabbed. In February, March, and April 2017, Antifa members attacked alt-right demonstrators at the University of California, Berkeley, using bricks, pipes, hammers, and homemade incendiary devices.42 In July 2019, William Van Spronsen, a self-proclaimed Antifa, attempted to bomb the U.S. Immigration and Customs Enforcement detention facility in Tacoma, Washington, using a propane tank but was killed by police.43


While religious terrorism is concerning, the United States does not face the same level of threat today from religious extremists—particularly those inspired by Salafi-jihadist groups such as the Islamic State and al-Qaeda—as some European countries.44 But Salafi-jihadists still pose a limited threat. In December 2019, Second Lieutenant Mohammed Saeed Alshamrani, a Saudi air force cadet training with the American military in Pensacola, Florida, killed three men and injured three others. He was inspired by al-Qaeda’s ideology, communicated with leaders of al-Qaeda in the Arabian Peninsula up until the attack, and joined the Saudi military in part to carry out a “special operation.”45

In addition, leaders of al-Qaeda and the Islamic State continue to encourage individuals in the West—including the United States—to conduct attacks.46 There are still perhaps 20,000 to 25,000 jihadist fighters in Syria and Iraq from the Islamic State and another 15,000 to 20,000 fighters from two al-Qaeda-linked groups: Hay’at Tahrir al-Sham and Tanzim Hurras al-Din.47 Over the next several months, more jihadists may enter the battlefield after escaping—or being released—from prisons run by the Syrian Democratic Forces in areas such as al-Hol, located in eastern Syria near the border with Iraq.48 In addition, there are still concerns about al-Qaeda and Islamic State groups operating in Yemen, Nigeria and neighboring countries, Somalia, Afghanistan, and other countries. In a May 2020 report, the United Nations concluded that al-Qaeda remains a serious threat and that the “senior leadership of Al-Qaida remains present in Afghanistan, as well as hundreds of armed operatives, Al-Qaida in the Indian Subcontinent, and groups of foreign terrorist fighters aligned with the Taliban.”49


Our data suggest that right-wing extremists pose the most significant terrorism threat to the United States, based on annual terrorist events and fatalities. Over the next year, the threat of terrorism in the United States will likely increase based on several factors, such as the November 2020 presidential election and the response to the Covid-19 crisis. These factors are not the cause of terrorism, but they are events and developments likely to fuel anger and be co-opted by a small minority of extremists as a pretext for violence.

First, the November 2020 presidential election will likely be a significant source of anger and polarization that increases the possibility of terrorism. Some—though not all—far-right extremists associate themselves with President Trump and may resort to violence before or after the election. As U.S. Department of Justice documents have highlighted, some far-right extremists have referred to themselves as “Trumpenkriegers”—or “fighters for Trump.”50 If President Trump loses the election, some extremists may use violence because they believe—however incorrectly—that there was fraud or that the election of Democratic candidate Joe Biden will undermine their extremist objectives. Alternatively, some on the far-left could resort to terrorism if President Trump is re-elected. In June 14, 2017, James Hodgkinson—a left-wing extremist—shot U.S. House Majority Whip Steve Scalise, U.S. Capitol Police officer Crystal Griner, congressional aide Zack Barth, and lobbyist Matt Mika in Alexandria, VA. A few months earlier, Hodgkinson wrote in a Facebook post that “Trump is a Traitor. Trump Has Destroyed Our Democracy. It’s Time to Destroy Trump & Co.”51 Tension on both the far right and far left has dramatically risen over the past several years.

Second, developments associated with Covid-19—such as prolonged unemployment or government attempts to close “non-essential” businesses in response to a second or third wave—could increase the possibility of terrorism. Some far-right extremists, for example, have threatened violence and railed against federal, state, and local efforts to take away their freedoms by requiring face coverings in public indoor settings, closing businesses, and prohibiting large gatherings to curb the spread of the virus. In March 2020, Timothy Wilson, who had ties to neo-Nazi groups, was killed in a shootout with FBI agents who were attempting to arrest him for planning to bomb a hospital in Missouri. Though he had been planning the attack for some time and had considered a variety of targets, he used the outbreak of Covid-19 to target a hospital in order to gain additional publicity. On the far left and far right, some anti-vaxxers—who oppose vaccines as a conspiracy by the government and pharmaceutical companies—have threatened violence in response to Covid-19 response efforts.52

Third, a polarizing event other than the presidential election—such as a school shooting or racially-motivated killing—could spark protests that extremists attempt to hijack. As highlighted in the introduction, extremists from all sides attempted to hijack the May and June 2020 protests in the United States as an excuse to commit acts of terrorism. In addition, far-right and far-left networks have used violence against each other at protests—such as in Berkeley, CA and Charlottesville, VA in 2017—raising concerns about escalating violence.

All parts of U.S. society have an important role to play in countering terrorism. Politicians need to encourage greater civility and refrain from incendiary language. Social media companies need to continue sustained efforts to fight hatred and terrorism on their platforms. Facebook, Google, Twitter, and other companies are already doing this. But the struggle will only get more difficult as the United States approaches the November 2020 presidential election—and even in its aftermath. Finally, the U.S. population needs to be more alert to disinformation, double-check their sources of information, and curb incendiary language.

Terrorism feeds off lies, conspiracies, disinformation, and hatred. Indian leader Mahatma Gandhi urged individuals to practice what he called “satyagraha,” or truth force. “Satyagraha is a weapon of the strong; it admits of no violence under any circumstance whatever; and it always insists upon truth,” he explained.53 That advice is just as important as it has ever been in the United States.

Seth G. Jones is the Harold Brown Chair and director of the Transnational Threats Project at the Center for Strategic and International Studies (CSIS) in Washington, D.C. Catrina Doxsee is a program manager and research associate with the Transnational Threats Project at CSIS. Nicholas Harrington is a research associate for the Transnational Threats Project at CSIS.

The authors give special thanks to James Suber and Grace Hwang for their research assistance and helpful comments, including their involvement in building the terrorism data set.

For an overview of the methodology used in compiling the data set, please see here.

This brief is made possible by general support to CSIS. No direct sponsorship contributed to this brief.

CSIS Briefs are produced by the Center for Strategic and International Studies (CSIS), a private, tax-exempt institution focusing on international public policy issues. Its research is nonpartisan and nonproprietary. CSIS does not take specific policy positions. Accordingly, all views, positions, and conclusions expressed in this publication should be understood to be solely those of the author(s).

© 2020 by the Center for Strategic and International Studies. All rights reserved.

Please consult the PDF for references.

Seth G. Jones
Senior Vice President; Harold Brown Chair; and Director, International Security Program
Catrina Doxsee
Associate Director and Associate Fellow, Transnational Threats Project

Nicholas Harrington