actual or threatened use of violence, directed by groups or individuals against noncombatants, to achieve political ends through intimidation. Under U.S. law, international terrorism involves the citizens or territory of more than one country, and noncombatants include unarmed or off-duty military personnel as well as civilians. Terrorist activities include bombings (including suicide bombings), skyjackings, abductions, and other actions that threaten or result in injury or death to noncombatants. A terrorist attack typically aims at terrorizing others who are not the direct (and usually random) victims. Targeted assassinations may be regarded as a kind of terrorism, though these will not generally be covered in this article. Violent acts by government troops and paramiitary forces against their own citizens, to suppress protest and opposition, or engage in a form of “ethnic cleansing,” may be considered terrorism, but will also not be specifically covered.

Activities by terrorist groups increased greatly from the late 1960s on, and especially after the turn of the century, spurred especially by Arab-Israeli tensions in the Middle East and by the growth of anti-Western radical Muslim fundamentalism; and their scope reached around the world. A notable example of terrorist success was the attack on the Pentagon near Washington, D.C., and New York City's World Trade Center, by Muslim extremists commandeering hijacked passenger jets, on Sept. 11, 2001; the death toll in those buildings and on 4 hijacked planes came to nearly 3000.

Dimensions of the Problem.

Because of the complex interconnections between terrorist groups, and because a terrorist group based in one country may draw financial support from other countries, even an incident that appears to be an instance of domestic terrorism may have international ramifications. Some groups finance their terrorist actions through drug smuggling, kidnapping, or other illegal activities. Other groups siphon funds donated for legitimate political, educational, and charitable purposes to support their terrorist agenda.

A special type of international terrorism is state-sponsored terrorism, which involves groups or acts that have the logistical or financial support of national governments. The United Nations Security Council in December 2000 imposed sanctions on the Taliban government in Afghanistan for providing safe haven to Islamic extremists, and armed forces led by the U.S. overthrew the Taliban regime in December 2001. The Security Council in November 2002 also called upon Iraq to cooperate with UN inspectors seeking to verify whether Iraq had weapons of mass destruction, or face “serious consequences.” Although no further UN resolution was passed, the U.S. and Britain, maintaining (wrongly) that Iraq had such weapons, and considering Iraq as noncompliant and as having possible terrorist ties, launched a massive air and ground campaign in Iraq that ousted the regime of Saddam Hussein in April 2003 (see below). But insurgents in both countries, sometimes arriving from other countries, continued to launch attacks, with large numbers of casualties, not only on armed forces but also on civilian populations, partly in hope of terrorizing others into eventual submission to their political goals.

In a report released early in 2006 the U.S. State Department listed six nations as state sponsors of terrorism and as such subject to various U.S. sanctions. The list was headed by Iran and Syria; also listed were Cuba, Libya, North Korea, and Sudan. But it was noted that Libya and Sudan were showing increased cooperation in the so-called global war on terror, and in mid-2006 Libya was dropped from the list.

The most widely active terrorist group in recent years has been al-Qaeda, a radical Islamic terrorist network established and funded in large part by Osama bin Laden, a wealthy Saudi businessman. Al-Qaeda maintained training camps in Afghanistan and N Iraq and was responsible for the Sept. 11 attacks, among other terrorist acts around the world. Among other active groups, the Liberation Tigers of Tamil Eelam (LTTE), operating in Sri Lanka, has launched some 200 suicide bombings in a two-decade civil war that has led to tens of thousands of deaths. Hamas, which grew out of Egypt's Muslim Brotherhood to become the largest and most influential Islamic resistance organization operating against Israel, has through its terrorist wing killed more than 500 people in hundreds of attacks in Israel and the occupied territories; it also operates an extensive network of social services to Palestinians and won a majority of seats in 2006 legislative elections for the Palestinian Authority. Hezbollah, an umbrella organization of radical Shiite groups, formed in 1982 in response to the Israeli invasion of Lebanon, has been responsible for more than 800 deaths, including more than 200 U.S. Marines killed in the 1993 bombing of their barracks in Lebanon; Hezbollah also has been involved in Lebanese politics. Under the U.S. Antiterrorism Act (1996), the U.S. State Department as of 2003 designated 36 groups as foreign terrorist organizations, making it illegal to provide funds for them and denying visas to their members. Fund-raising for many Middle East groups linked to support for terrorism has been banned by the U.S. since 1995.

A 2006 report on international terrorism by the U.S. State Department counted more than 11,000 terrorist attacks around the world in 2005 (about half of them producing casualties), up from 3168 in 2004 and about 208 in 2003; the number of people killed in 2005 was estimated at 14,602.

Origins and Development of International Terrorism.

Terrorism is a recognized phenomenon in the context of political and social upheaval and has occurred throughout history. In the 19th century, anarchists (see Anarchism) in Italy, Switzerland, and Spain used terrorism, as did their counterparts in France. The Russian revolutionary movement before World War I had a strong terrorist element. After World War II some forms of terrorism were used by left-wing groups, as well as right-wing groups, to press for changes in government policies.

The wave of international terrorism that developed after the mid-1960s differed from earlier ones in its broader ramifications and greater impact. Several elements combined to make international terrorism easier and more effective: technological advances, resulting in both greater destructiveness and smaller size of weapons; the means available to terrorists for quick movement and rapid communication; and the extensive worldwide connections of the chosen victims.

Middle East.

The unresolved Middle East conflict between the Arab nations and Israel was an essential element in the terrorist wave that began in the 1960s. Radical Jewish groups such as the Stern Gang and the Irgun Zvai Leumi resorted to terrorism in their struggle for an independent Israel in the late 1940s. Their Arab adversaries in the 1960s and beyond chose to use terrorism more systematically. The expulsion of Palestinian guerrillas from Jordan in September 1970 was commemorated by the creation of an extremist terrorist organization called Black September, which was responsible for the deadly attack on Israeli athletes at the 1972 Munich Olympics. The Palestine Liberation Organization (PLO), or groups under its umbrella, conducted commando and terrorist operations against Israeli targets in Israel and around the world, in the 1960s and 1970s and later. Prior to the fall of the Soviet Union, leftist groups associated with the PLO, such as the Popular Front for the Liberation of Palestine, were highly active. The PLFP participated, with West German terrorists, in the June 1976 hijacking of an Air France jet that was forced to land in Entebbe, Uganda. In a famous raid, Israeli and Ugandan troops rescued 103 hostages on the ground there, but 32 people were killed.

The PLO and Israel signed the so-called Oslo accords in 1993, initiating the Middle East peace process, and in 1994 the U.S. removed the PLO from its list of terrorist groups. But the PLO did not fully abandon its armed struggle, with, for example, a militia offshoot known as the Al Aqsa Martyrs Brigade eventually launching attacks against civilian targets in israel. Hamas, which had repudiated the Oslo accords, continued its militancy and also bested the more moderate Al Fatah faction of the PLO by winning a majority in Palestinian legislative elections in 2006.

Germany and Italy.

The spread of terrorism beyond the Middle East in the 1960s was most conspicuous in West Germany and Italy. Inspired by vague Communist ideologies (see Communism) and typically supported by sympathizers in the affluent middle classes, the terrorists aimed to bring about the collapse of the state by provoking its violent, self-destructive reaction.

In West Germany, the so-called Red Army Faction, better known as the Baader-Meinhof Gang, robbed numerous banks and raided U.S. military installations. Its most spectacular exploits were the 1977 kidnapping and murder of a prominent industrialist, Hans-Martin Schleyer (1915–77), and the subsequent hijacking by Arab sympathizers of a Lufthansa airliner to Mogadishu, Somalia. The gang frequently cooperated with Palestinian terrorists, notably in the murder of Israeli athletes at the Olympic Games in Munich in 1972. By the late 1970s, most activists of the Red Army Faction were either imprisoned or dead.

The strength of the Italian terrorists, the most prominent of whom were the Red Brigades, may stem from the country's anarchist tradition and its political instability. Their activities culminated in the 1978 kidnapping and murder of former prime minister Aldo Moro. Left-wing terrorism subsequently declined, thanks to police measures, although it by no means disappeared. Right-wing terrorism, however, seemed to increase in Italy, as highlighted by the bombing in 1980 of the Bologna railroad station. The historic Uffizi Gallery in Florence was among the targets of a series of terrorist bombings in 1993 alleged to be the work of the Mafia.

Spain.

The Basque separatist group ETA (Euskadi Ta Askatasuna, “Basque Homeland and Liberty”) was founded in 1959. Since the early 1960s, ETA car bombings and other attacks have claimed the lives of at least 800 people; the group's most prominent assassination victim was Premier Luis Carrero Blanco (1903–73). The ETA's support has waned in recent years, in part because of steps by the central government to encourage Basque regional autonomy and economic development, and in 2006 the ETA and the Spanish government reached a cease-fire agreement. (See also Basques; Spain).

The deadliest terrorist attack in Spanish history occurred on March 11, 2004, when 10 bombs exploded on four commuter trains in Madrid, killing about 200 people and injuring many hundreds more. Spain's conservative government initially blamed ETA for the attack; subsequent investigations focused on Islamic radicals, mostly Moroccan, who were allegedly retaliating for the Spanish government's support of the U.S-led invasion of Iraq a year earlier (see below). In nationwide parliamentary elections—which took place, as scheduled, on March 14—Spanish voters responded to the bombings by electing a Socialist Workers party government, which withdrew Spain's troops from Iraq.

Japan.

The Japanese Red Army terrorist organization, founded in 1971 and allied with hard-line Palestinian factions, was a deadly force during the 15-year civil war in Lebanon. Once one of the most feared terrorist groups in the world, with hundreds of members, the organization was severely weakened in the 1990s. In March 1995, another Japanese group made headlines around the world when 12 people were killed and thousands injured from the release of deadly sarin gas in the Tokyo subway system by members of Aum Shinrikyo, a religious cult (see Chemical and Biological Warfare).

Northern Ireland.

The Irish Republican Army (IRA) was fighting British rule in Ireland from before the establishment of the republic in 1949. In the late 1960s, when minority Roman Catholics began a forceful campaign for improved economic and political status in Protestant-dominated Northern ireland, support for the IRA grew and IRA attacks against Protestant militants and the British army escalated; more then 1800 people were killed in Britain and Northern Ireland during the violence that followed over the next few decades. Following a 1998 peace agreement between Britain and the IRA political party Sinn Fein, public support for militancy declined; ultimately in the early 2000s, the IRA took steps to disarm and progress was being made toward establishing a power-sharing government of Protestants and Catholics in Northern Ireland.

Latin America.

Terrorist movements in Latin America had their origins in long-standing local traditions of political violence. The main new development was the rise in so-called urban guerrilla movements, as terrorist activities shifted from the countryside to the sprawling cities. In the 1990s some members of the cocaine cartel in Colombia used terrorist tactics to get the government to curtail enforcement of the anti-drug-trafficking laws. In Peru, the Shining Path (Sendero Luminoso), a leftist guerrilla group, used violence in an attempt to address the country's economic hardships in the early 1990s. In December 1996, Tupac Amaru guerrillas took some 600 hostages in Lima, Peru's capital, demanding the release of their imprisoned comrades. All but 70 hostages were freed by March 1997; the standoff ended in a shootout in April, during which all 14 rebels, 1 hostage, and 2 soldiers were killed.

Russia.

Terrorist outbreaks within Russia during the late 1990s and early 2000s stemmed primarily from the war fought between Russian troops and Muslim rebels for control over the breakaway republic of Chechnya. Among many other terrorist incidents, Chechen rebels were blamed for explosions in three apartment buildings in Moscow and Volgodonsk during September 1999 that killed about 300 people. In October 2002 about 50 armed Chechen guerrillas seized a Moscow theater and held more than 800 persons hostage for three days; an assault by Russian special forces that began by pumping in an aerosol anesthetic through ventilation ducts to immobilize the terrorists, led to the deaths of 129 hostages and nearly all the guerrillas. In another major incident, Chechen militants seized a school in Beslan, northern Ossetia (part of Russia) in September 2004; Russian troops stormed the school after three days, and some 300 children and adults, including the 27 hostage takers, were killed.

The U.S. as Target of Terrorism.

Since the 1940s, pro-independence Puerto Ricans in such groups as the U.S.-based Armed Forces of National Liberation (Fuerzas Armadas de Liberación Nacional, or FALN) have occasionally engaged in terrorism to press their case against the U.S. government. A much larger incident was an act of home-grown terrorism. In April 1995, a truck bomb explosion in Oklahoma City, Okla., destroyed the Alfred P. Murrah Federal Building, killing 168 people. Timothy McVeigh (1968–2001), a U.S. Army veteran with anti-government beliefs, was convicted of murder and conspiracy in the bombing in June 1997; he was executed four years later. Terry Nichols (1955–    ) was convicted in December 1997 of conspiracy and involuntary manslaughter as a co-conspirator and sentenced to life in prison without parole; in 2004 he was also found guilty of murder by a state jury, but escaped the death penalty.

But the greatest threat by far has come from the Middle East, where many groups consider the U.S. and other Western nations their enemy. Several instances of hijacking by Arab groups brought tighter security to travel terminals around the world. In 1988, however, a bomb destroyed Pan American Flight 103 over Lockerbie, Scotland, killing all 259 people on board and 11 on the ground. The U.S. Central Intelligence Agency in 1991 charged Libyan agents with the crime. Eight years later, the Libyan government turned over two suspects for trial in the Netherlands under Scottish law; one was found guilty of murder and sentenced to prison, while the other was acquitted. In 2003 the Libyan government renounced terrorism and reached agreement on compensation for the families of the Lockerbie victims and of 170 people who died when UTA Flight 772 was downed over Niger in 1989. The U.S. subsequently lifted sanctions against Libya and removed it from a list of nations that sponsor terrorism.

Al-Qaeda Attacks.

In 1993, a bomb exploded in an underground garage at the World Trade Center in New York City killing six people. The following year, four Arab defendants were convicted in the bombing, which was linked to the al-Qaeda terrorist network, and sentenced to prison terms of 240 years each. Ramzi Ahmed Yousef (1969–    ), charged with masterminding it, was captured in 1995 and convicted along with a co-defendant in 1997; he received the same 240 years for the Trade Center attack, as well as life imprisonment for the 1994 bombing of a Philippine Airlines plane.

On Aug. 7, 1998, two truck bombs detonated within minutes of each other at U.S. embassies in Nairobi, Kenya, and Dar es-Salaam, Tanzania, killing 224 people, including 12 Americans, and wounding more than 5000. The U.S. launched cruise missile attacks on sites in Afghanistan and Sudan, claiming the sites were associated with al-Qaeda. Osama bin Laden, the head of al-Qaeda, reportedly had a hand in the embassy bombings, as well as in the 1993 World Trade Center blast, and in the attempted assassination of Egyptian President Hosni Mubarak in Ethiopia in June 1995, truck bomb explosion that killed 19 Americans at a military base in Dhahran, Saudi Arabia, in June 1996, and a bomb attack on the destroyer U.S.S. Cole that killed 17 American sailors and wounded 39 others in Aden, Yemen, in October 2000.

U.S. officials also labeled bin Laden's al-Qaeda network as the prime suspect in the coordinated terrorist attacks of Sept. 11, 2001, which began with the hijacking of four civilian jetliners. Two of the aircraft were deliberately flown into the twin towers of the 110-story World Trade Center; a third rammed Department of Defense headquarters at the Pentagon; a fourth crashed near Shanksville, Pa., about 80 mi (50 km) SE of Pittsburgh. More than 2700 persons were killed in the World Trade Center attack, many of them trapped when the twin towers collapse. In all, it is believed 2973 people were killed in the attacks, including 33 crew members and 213 innocent passengers, plus 19 hijackers, on board the four aircraft, and 125 persons on the ground at the Pentagon.

“War Against Terrorism.”

Responding to the 2001 attacks, the U.S. launched a “war against terrorism,” focusing on al-Qaeda and allied groups. In addition to dismantling the Taliban regime and destroying al-Qaeda training camps in Afghanistan, U.S. forces conducted antiterrorist operations in Yemen and assisted local troops in fighting guerrillas in the Philippines and the former Soviet republic of Georgia. The U.S.-led invasion of Iraq ouster in spring 2003 led to the ouster of Iraqi dictator Saddam Hussein, whom the U.S. had branded as a sponsor of terrorism, though he was not found to have had clear links with terrorist plots and operations; he was captured in December 2003 and, after a trial by an Iraqi court, executed for a 1982 massacre in the Shiite village of Dujail. The U.S. also sought to step up pressure on two of Iraq's neighbors, Iran and Syria, which the U.S. has consistently accused of harboring and supporting terrorists, but did not appear to make much progress in this regard.

On the domestic front, the U.S. established the cabinet-level Department of Homeland Security and instituted a color-coded terror risk advisory system, ranging from green (low risk of terrorist attack) to red (severe risk). Some U.S. countermeasures—notably the prolonged detention at the U.S. naval base at Guantánamo Bay, Cuba, of more than 600 foreign nationals, most of them captured during the Afghan war—were criticized by the human rights organization Amnesty International, and by other critics at home and abroad, while being defended by the government as necessary. Other governments also intensified their antiterrorist activities, in some cases allegedly committing human rights abuses in the process. Many, though not all, governments cooperated or sought to cooperate in rooting out terrorists plotting to export violence and in seeking out fugitives wanted for terrorist acts in other countries.

A number of top al-Qaeda operatives were eventually captured, and apparent plots forestalled in several countries, leading some to speculate that the organization had been severely weakened, but bin Laden remained at large, certain areas, including the Afghanistan-Pakistan border, appeared to be providing sanctuary for terrorists and would-be terrorists, and reports suggested that small cells of al-Qaeda operatives and like-minded terrorists were increasingly active in local areas, without needing direction or support from the al-Qaeda hierarchy. While years passed by with no terrorist action on a scale comparable to the Sept. 11 attacks, there were sporadic major incidents around the world.

Among other attacks, in April 2002, a tanker truck filled with natural gas exploded outside a historic synagogue on the island of Jarbah, Tunisia, killing 17 people, including 12 German tourists. In October 2002, near-simultaneous blasts in the entertainment district of Bali, Indonesia, claimed the lives of some 200 people, most of them foreign tourists; the following month, in Kenya, suicide bombers killed 12 Kenyans and 3 Israeli tourists at an Israeli-owned seaside resort hotel, and antiaircraft missiles were fired at an Israeli-bound charter jet taking off from Mombasa. Multiple terrorist strikes against civilian targets in Saudi Arabia and Morocco were carried out in May 2003. The Saudi bombings, aimed at westerners living in Riyadh, claimed the lives of 25 people, in addition to the 9 suicide bombers; five explosions, detonated within half an hour, killed 31 people, along with the 12 suicide bombers, in Morocco a few days later. Al-Qaeda and its allies were believed to be responsible for all of these attacks.

Meanwhile, Islamic extremists, Hussein loyalists, and their allies, including persons emigrating from abroad, used car bombings and other guerrilla tactics to continue an insurgency against U.S. occupation forces in Iraq and, after June 2004, against an interim Iraqi administration, often targeting civilian populations, which sustained heavy casualties. Among many notable incidents in Iraq, United Nations headquarters in Beirut were hit by a truck bomb in August 2003, killing 22 people including the UN ambassador to Iraq.

For further information on this topic, see the Bibliography, section Terrorism.