Domestic terrorism in the United States consists of incidents confirmed as terrorist acts. These attacks are considered domestic because they were carried out by U.S. citizens or U.S. permanent residents.
The statutory definition of domestic terrorism in the United States has changed many times over the years; also, it can be argued that acts of domestic terrorism have been occurring since long before any legal definition was set forth.
Under current United States law, set forth in the USA PATRIOT Act, acts of domestic terrorism are those which: "(A) involve acts dangerous to human life that are a violation of the criminal laws of the United States or of any State; (B) appear to be intended – (i) to intimidate or coerce a civilian population; (ii) to influence the policy of a government by intimidation or coercion; or (iii) to affect the conduct of a government by mass destruction, assassination, or kidnapping; and (C) occur primarily within the territorial jurisdiction of the United States."  
While the PATRIOT Act defines "domestic terrorism" for the purposes of authorizing law enforcement investigations, no federal criminal offense exists which is referred to as "domestic terrorism". While international terrorism ("acts of terrorism transcending national boundaries") is a defined crime in federal law, acts of domestic terrorism are charged under specific laws, such as killing federal agents or "attempting to use explosives to destroy a building in interstate commerce".
Citizens suspected of terrorism are usually investigated and arrested by federal law enforcement, such as the FBI. For instance, from 2016 to 2018, the FBI arrested 355 suspects on domestic terrorism related charges. Per the FBI, the vast majority were motivated by racist and anti-government ideology.
Anti-abortion violence, considered a form of terrorism, is often committed in the United States against individuals and organizations that provide abortions or abortion counseling. Incidents have included crimes against people, such as murder, assault, kidnapping, and stalking; crimes affecting both people and property, such as arson or bombing; and property crimes such as vandalism. Perpetrators may defend their actions as necessary to protect fetuses, and are often motivated by their Christian beliefs, leading to anti-abortion violence's identification as Christian terrorism; it is also associated with antifeminism.
Notable incidents of anti-abortion violence include the murders of a number of doctors and clinic staff in the 1990s.
According to the FBI in June 2008, eco-terrorists and extreme animal rights activists represented "one of the most serious domestic terrorism threats in the U.S. today". They committed over 2,000 crimes and caused over $110 million in damages since 1979, against targets including lumber companies, animal testing facilities and genetic research firms. However, no human casualties have been reported.
Right-wing terrorism or far-right terrorism is motivated by a variety of different right-wing and far-right ideologies, most prominently by neo-Nazism, neo-fascism, white nationalism, white separatism, ethnonationalism, religious nationalism, and anti-government patriot/sovereign citizen beliefs.
Alpha 66 (still existent) and Omega 7 (now defunct) were two affiliated Cuban exile action groups who have carried out many bombings and acts of sabotage. While many of these attacks have historically been directed at Cuba and the Castro government, many of them occurred domestically, especially during the period of Cuba-US diplomacy and negotiations in the 1970s known as "el Diálogo" (the dialogue) when powerful anti-Castro figures in Miami attempted to terrorize those in their community who favored a more moderate approach. Luciano Nieves, for instance, was killed for advocating peaceful coexistence with Cuba. WQBA-AM news director Emilio Milian lost his legs in a car bomb after he publicly condemned Cuban exile violence. These cases of terrorism were documented extensively in the book Miami by Joan Didion. Human Rights Watch released a report in 1992 in which it claimed that the more extreme exiles have created a political environment in Miami where "moderation can be a dangerous position."
Animal Liberation Front (ALF) is a name used internationally by activists who engage in direct action against persons and/or organizations which the activists perceive are harming animals. This includes removing animals from laboratories and fur farms, and sabotaging facilities involved in animal testing and other animal-based industries. According to ALF statements, any act that furthers the cause of animal liberation, where all reasonable precautions are taken not to endanger life, may be claimed as an ALF action.
The Army of God (AOG) is a loose network of individuals and groups connected by ideological affinity and the determination to use force to end abortion in the United States. Acts of anti-abortion violence increased in the mid-1990s culminating in a series of bombings by Eric Robert Rudolph, whose targets included two abortion clinics, a gay and lesbian night club, and the 1996 Olympics in Atlanta. Letters sent to newspapers claim responsibility for the bombing of the abortion clinics in the name of the Army of God.
Aryan Nations (AN) is a white nationalist neo-Nazi organization founded in the 1970s by Richard Girnt Butler as an arm of the Christian Identity group known as the Church of Jesus Christ-Christian. As of December 2007 there were two main factions that claimed descent from Butler's group. The Aryan Nations has been called a "terrorist threat" by the FBI, and the RAND Corporation has called it the "first truly nationwide terrorist network" in the United States.
The Atomwaffen Division (AWD) or simply Atomwaffen is a neo-Nazi organization based in Florida that promotes former American Nazi Party and National Socialist Liberation Front (NSLF) member convict James Mason's Siege and "Universal Order" ideology as well as race war against minorities, Jews, and LGBT people. Atomwaffen also draws influence from Nazi esotericism and the occult. The group has about 80 full members and a "large" amount of initiates and 20 cells across 23 states in America. The organization also has a United Kingdom branch called the Sonnenkrieg Division (SKD), a Baltic branch called Feuerkrieg Division (FKD), a presence in Canada by a group called Northern Order and one located in Germany. The organization has been responsible for the deaths of eight people most notably the Murder of Blaze Bernstein a gay Jewish California student and the killings of Jeremy Himmelman and Andrew Oneschuk.
A splinter group made up of the more radical members of the Black Panther Party, the Black Liberation Army (BLA) sought to overthrow the US government in the name of racial separatism and Marxist ideals. The Fraternal Order of Police blames the BLA for the murders of 13 police officers. According to a Justice Department report on BLA activity, the group was suspected of involvement in over 60 incidents of violence between 1970 and 1980.
The Covenant, The Sword, and the Arm of the Lord (CSA) was a radical Christian Identity organization formed in 1971 in the small community of Elijah in southern Missouri, United States. One of its members, Richard Wayne Snell was responsible for the murder of a pawnshop owner and a Missouri state trooper. The CSA collapsed following an FBI and ATF siege in 1985.
The Jewish Defense League (JDL) was founded in 1968 by Rabbi Meir Kahane in New York City. FBI statistics show that from 1980 to 1985, 15 terrorist attacks were attempted in the U.S. by JDL members. The FBI's Mary Doran described the JDL in 2004 Congressional testimony as "a proscribed terrorist group". The National Consortium for the Study of Terror and Responses to Terrorism states that during the JDL's first two decades of activity it was an "active terrorist organization." Kahane later founded the far right Israeli political party Kach.
During reconstruction at the end of the Civil War the original KKK used domestic terrorism against the federal government and against freed slaves. During the 20th century, leading up to the Civil Rights Movement, unrelated Ku Klux Klan (KKK) groups used threats, violence, arson, and murder to further their anti-Black, anti-Catholic, anti-Communist, anti-immigrant, anti-Semitic, homophobic and white-supremacist agenda. Other groups with agendas similar to the Ku Klux Klan include neo-Nazis, white power skinheads, and other far-right movements.
The May 19 Coalition (also variously referred to as the May 19 Communist Coalition, May 19 Communist Organization, and various alternatives of M19CO), was a U.S.-based, self-described revolutionary organization formed by members of the Weather Underground Organization. The group was originally known as the New York chapter of the Prairie Fire Organizing Committee (PFOC), an organization devoted to legally promoting the causes of the Weather Underground. This was part of Prairie Fire Manifesto change in Weather Underground Organization strategy, which demanded both aboveground mass and clandestine organizations. The role of the clandestine organization would be to build the "consciousness of action" and prepare the way for the development of a people's militia. Concurrently, the role of the mass movement (i.e., above ground Prairie Fire Collective) would include support for, and encouragement of, armed action. Such an alliance would, according to Weather, "help create the 'sea' for the guerrillas to swim in."
The Order, also known as the Brüder Schweigen or Silent Brotherhood, was a white nationalist revolutionary group active in the United States between 1983 and 1984. It is probably best known for the 1984 murder of radio talk show host Alan Berg. The group also carried out several bank and car robberies, three murders, and money counterfeiting until its leader, Robert Jay Mathews, was killed in a shootout with FBI agents on Whidbey Island, Washington, in December 1984.
The Phineas Priesthood (Phineas Priests) is a Christian Identity movement that opposes interracial sex, the mixing of races, homosexuality, and abortion. It is also marked by anti-Semitism, anti-multiculturalism, and opposition to taxation. It is not considered an organization because it is not led by a governing body, there are no gatherings, and there is no membership process. One becomes a Phineas Priest by simply adopting the beliefs of the Priesthood and acting upon those beliefs. Members of the Priesthood are often called terrorists for, among other things, planning to blow up FBI buildings, abortion clinic bombings, and bank robberies.
The Symbionese Liberation Army (SLA) was an American self-styled, far left "urban guerrilla warfare group" that considered itself a revolutionary vanguard army. The group committed bank robberies, two murders, and other acts of violence between 1973 and 1975. Among their most notorious acts was the kidnapping of the newspaper heiress Patty Hearst.
The United Freedom Front (UFF) was a small American Marxist organization active in the 1970s and 1980s. It was originally called the Sam Melville/Jonathan Jackson Unit, and its members became known as the Ohio 7 when they were brought to trial. Between 1975 and 1984 the UFF carried out at least 20 bombings and nine bank robberies in the northeastern United States, targeting corporate buildings, courthouses, and military facilities. Brent L. Smith describes them as "undoubtedly the most successful of the leftist terrorists of the 1970s and 1980s." The group's members were eventually apprehended and convicted of conspiracy, murder, attempted murder, and other charges. Two, Tom Manning and Jaan Laaman, remain incarcerated today.
The Weather Underground Organization was a far left organization active from 1969 to 1975. It originated in 1969 as a faction of Students for a Democratic Society (SDS) composed for the most part of the national office leadership of SDS and their supporters. The group collapsed shortly after the U.S. withdrawal from Vietnam in 1975.
The Mountain Meadows massacre was a series of attacks on the Baker–Fancher emigrant wagon train, at Mountain Meadows in southern Utah. The attacks began on September 7 and culminated on September 11, 1857, resulting in the mass slaughter of the emigrant party by members of the Utah Territorial Militia from the Iron County district, a Mormon group, together with some Paiute Native Americans. Intending to leave no witnesses and thus prevent reprisals, the perpetrators killed all the adults and older children – about 120 men, women, and children in total. Seventeen children, all younger than seven, were spared.
The Milwaukee Police Department bombing was a November 24, 1917, bomb attack that killed ten people including nine members of local law enforcement. The perpetrators were never caught but are suspected to be an anarchist terrorist cell operating in the United States in the early 20th century. The target was initially an evangelical church in the Third Ward and only killed the police members when the bomb was brought to the police station by a concerned member of the public.
The Wall Street bombing was a terrorist incident on September 16, 1920, in the Financial District of New York City. A horse-drawn wagon filled with 100 pounds (45 kg) of dynamite was stationed across the street from the headquarters of the J.P. Morgan Inc. bank. The explosion killed 38 and injured 400. Even though no one was found guilty, it is believed that the act was carried out by followers of Luigi Galleani.
On May 31 and June 1, 1921, a white mob started the Tulsa race massacre attacking residents and businesses of the African-American community known as Black Wall Street, in the Greenwood area in Tulsa, Oklahoma, in what is considered one of the worst incidents of racial violence in United States History. The attack, carried out on the ground and by air, destroyed more than 35 blocks of the district, did $30 million (2017 dollars) in damages, left 10,000 people homeless and up to 300 dead in a town considered the wealthiest black community in the nation.
On Sunday, September 15, 1963, members of the United Klans of America set a bomb consisting of a timing device and fifteen sticks of dynamite to explode at a historically-black church in Birmingham, Alabama, that was a local focus of the Civil Rights struggle. The explosion killed four girls between the ages of 11 and 14 and did much other local damage. Three perpetrators were eventually caught years later and sentenced to life imprisonment for their roles. There had been other bombings in Birmingham, then grimly known as "Bombingham" for such attacks.
From 1978 to 1995, Harvard University graduate and former mathematics professor Theodore "Ted" Kaczynski – known by the codename "UNABOM" until his identification and arrest by the FBI – carried out a campaign of sending letterbombs to academics and various individuals particularly associated with modern technology. In 1996, his manifesto was published in The New York Times and The Washington Post, under the threat of more attacks. The bomb campaign ended with his capture.
In a 2004 congressional testimony, John S. Pistole, Executive Assistant Director for Counterterrorism and Counterintelligence for the Federal Bureau of Investigation described the JDL as "a known violent extremist Jewish Organization." FBI statistics show that, from 1980 through 1985, there were 18 terrorist attacks in the U.S. committed by Jews; 15 of those by members of the JDL. Mary Doran, an FBI agent, described the JDL in a 2004 Congressional testimony as "a proscribed terrorist group". Most recently, then-JDL Chairman Irv Rubin was jailed while awaiting trial on charges of conspiracy in planning bomb attacks against the King Fahd Mosque in Culver City, California, and on the office of Arab-American Congressman Darrell Issa. In its report, Terrorism 2000/2001, the FBI referred to the JDL as a "violent extremist Jewish organization" and stated that the FBI was responsible for thwarting at least one of its terrorist acts.
This truck bomb attack by Timothy McVeigh and Terry Nichols killed 168 people on April 19, 1995 – the deadliest domestic-based terrorist attack in the history of the United States since the era of mass lynchings and race riots. It inspired improvements to United States federal building security.
The Centennial Olympic Park bombing was a terrorist bombing on July 27, 1996, in Atlanta, Georgia, during the 1996 Summer Olympics, the first of four committed by Eric Robert Rudolph, former explosives expert for the United States Army. Two people died, and 111 were injured.
On August 5, 2012, Wade Michael Page fatally shot six people (including himself) and wounded four others in a mass shooting at a Sikh temple in Oak Creek, Wisconsin. Page was an American white supremacist and a United States Army veteran from Cudahy, Wisconsin, who was a member of the neo-Nazi skinhead Hammerskin Nation. All of the dead were members of the Sikh faith.
On April 15, 2013, two homemade bombs detonated 12 seconds and 210 yards apart at 2:49 p.m., near the finish line of the annual Boston Marathon, killing three people and injuring several hundred others, including 16 who lost limbs. Kyrgyz-American brothers Dzhokhar Tsarnaev and Tamerlan Tsarnaev were apprehended and claimed to have been motivated by radical Islamist beliefs.
On June 17, 2015, Dylann Roof, a 21-year-old white supremacist, went into the Emanuel African Methodist Episcopal Church in Charleston, South Carolina, and shot and killed nine people including South Carolina senator Clementa C. Pinckney. Roof was known to be a white supremacist who admired Apartheid South Africa and Rhodesia and owned a website with a manifesto both called The Last Rhodesian in which he outlined his views toward blacks, among other peoples.
On December 2, 2015, 14 people were killed and 24 injured in a mass shooting at the Inland Regional Center in San Bernardino, California, United States. Syed Rizwan Farook and Tashfeen Malik targeted a San Bernardino County Department of Public Health training event and holiday party of about 80 employees in a rented banquet room. Farook was an American-born citizen of Pakistani descent, while his wife was a Pakistani-born legal resident of the U.S. He had attended the event as an employee before the shooting. Both had become radicalized through jihadist material on the internet, and stockpiled supplies in their home.
In the early hours of June 12, 2016, 49 people were killed and 53 were injured in a mass shooting at the Pulse nightclub in Orlando, Florida. The perpetrator, 29-year-old Omar Mateen, was a security guard and person of interest to the FBI in 2013 and 2014. At the time, this event was the deadliest mass shooting in United States history by a single gunman, later eclipsed by the 2017 Las Vegas shooting on October 1, 2017. Additionally, it was the deadliest confirmed terrorist attack on U.S. soil since the 9/11 attacks and the deadliest attack against LGBT people in U.S. history.
While the annual Congressional Baseball Game for Charity was going on, James Thomas Hodgkinson opened fire on Republican Congressmen and Congresswomen on the field such as U.S. House Majority Whip Steve Scalise, U.S. Capitol Police Officer Crystal Giner, congressional aide Zack Barth and lobbyist Matt Mika, resulting in 6 getting injured (4 critically) and the perpetrator getting killed. James Thomas Hodgkinson prior to the shooting was a supporter of Democratic presidential candidate Bernie Sanders and had liked various left-wing/liberal and anti-Donald Trump/anti-Republican Facebook pages.
During the Charlottesville riots/Unite the Right rally on August 11-12, 2017 in Charlottesville, Virginia, by neo-Nazis, neo-fascists, white nationalists, alt-righters, Southern nationalists and Ku Klux Klansmen, Vanguard America (VA) member James Alex Fields drove his car into counter-protesters, killing 1 named Heather Heyer and injuring 28 others.
On October 27, 2018, 11 people died and 6 more were injured at the Tree of Life - Or L'Simcha Congregation in Pittsburgh, Pennsylvania by Robert Bowers a user of Gab. The attack was motivated by anti-Semitism and a belief in the white genocide conspiracy theory.
On March 24, 2019, a mosque in Escondido, California, was set on fire; no one was injured and the fire was contained without major damage. The following month, on April 27, 2019, an elderly Jewish woman named Lori Gilbert-Kaye was killed and three others (including Rabbi Yisroel Goldstein) were injured at the Chabad of Poway synagogue in Poway, California. The accused shooter, John T. Earnest, blamed Jews for "white genocide" and other ills in an anti-Semitic and racist open letter on 8chan confessing to the mosque arson and citing inspiration from the Christchurch mosque shooter Brenton Harrison Tarrant and Pittsburgh synagogue shooting perpetrator Robert Bowers.
On August 3, 2019, a domestic terrorist attack/mass shooting occurred at a Walmart store in El Paso, Texas, killing 22 people and injuring 24 others. The attack was carried out by Patrick Crusius, who wrote a manifesto titled The Inconvenient Truth and posted it on 8chan where he cited a supposed "Hispanic invasion of Texas" and "simply trying to defend my country from ethnic and cultural replacement brought on by an invasion" as motivations as well as praising the perpetrator of the Christchurch, New Zealand, mosque shootings and read his manifesto The Great Replacement.