terrorism, the threat or use of violence, often against the civilian population, to achieve political or social ends, to intimidate opponents, or to publicize grievances. The term dates from the Reign of Terror (1793-94) in the French Revolution but has taken on additional meaning in the 20th cent. Terrorism involves activities such as assassinations, bombings, random killings, and hijackings. Used for political, not military, purposes, and most typically by groups too weak to mount open assaults, it is a modern tool of the alienated, and its psychological impact on the public has increased because of extensive coverage by the media. Political terrorism also may be part of a government campaign to eliminate the opposition, as under Hitler, Mussolini, Stalin, and others, or may be part of a revolutionary effort to overthrow a regime. Terrorist attacks also are now a common tactic in guerrilla warfare. Governments find attacks by terrorist groups difficult to prevent; international agreements to tighten borders or return terrorists for trial may offer some deterrence.

Terrorism reaches back to ancient Greece and has occurred throughout history. Terrorism by radicals (of both the left and right) and by nationalists became widespread after World War II. Since the late 20th cent. acts of terrorism have been associated with the Italian Red Brigades, the Irish Republican Army, the Palestine Liberation Organization, Peru's Shining Path, Sri Lanka's Liberation Tigers of Tamil Eelam, the Weathermen and some members of U.S. "militia" organizations, among many groups. Religiously inspired terrrorism has also occurred, such as that of extremist Christian opponents of abortion in the United States; of extremist Muslims associated with Hamas, Osama bin Laden's Al Qaeda, and other organizations; of extremist Sikhs in India; and of Japan's Aum Shinrikyo, who released nerve gas in Tokyo's subway system (1995).

In 1999 the UN Security Council unanimously called for better international cooperation in fighting terrorism and asked governments not to aid terrorists. The Sept. 11, 2001, attacks by Al Qaeda on the World Trade Center and the Pentagon—the most devastating terrorist attacks in history—prompted calls by U.S. political leaders for a world "war on terrorism." Although the U.S. effort to destroy Al Qaeda and overthrow the Afghani government that hosted it was initially successful, terrorism is not a movement but a tactic used by a wide variety of groups, some of which are regarded (and supported) as "freedom fighters" in various countries or by various peoples. So-called state-sponsored terrorism, in which governments provide support or protection to terrorist groups that carry out proxy attacks against other countries, also complicates international efforts to end terror attacks, but financial sanctions have been placed by many countries on organizations that directly or indirectly support terrorists. The 2001 bioterror attacks in which anthrax spores were mailed to various U.S. media and government offices may not be linked to the events of September 11, but they raised specter of biological and chemical terrorism and revealed the difficulty of dealing with such attacks.

Systematic use of violence to create a general climate of fear in a population and thereby to bring about a particular political objective. It has been used throughout history by political organizations of both the left and the right, by nationalist and ethnic groups, and by revolutionaries. Although usually thought of as a means of destabilizing or overthrowing existing political institutions, terror also has been employed by governments against their own people to suppress dissent; examples include the reigns of certain Roman emperors, the French Revolution (see Reign of Terror), Nazi Germany, the Soviet Union under Stalin, and Argentina during the “dirty war” of the 1970s. Terrorism's impact has been magnified by the deadliness and technological sophistication of modern-day weapons and the capability of the media to disseminate news of such attacks instantaneously throughout the world. The deadliest terrorist attack ever occurred in the United States on Sept. 11, 2001 (see September 11 attacks), when members of al-Qaeda terrorist network hijacked four commercial airplanes and crashed two of them into the twin towers of the World Trade Center complex in New York City and one into the Pentagon building near Washington, D.C.; the fourth plane crashed near Pittsburgh, Pa. The crashes resulted in the collapse of much of the World Trade Center complex, the destruction of part of the southwest side of the Pentagon, and the deaths of some 3,000 people.

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or ecological terrorism or environmental terrorism

The destruction, or the threat of destruction, of the environment in order to intimidate or coerce governments. The term has also been applied to crimes committed against companies or government agencies in order to prevent or interfere with activities allegedly harmful to the environment. Ecoterrorism includes threats to contaminate water supplies or to destroy or disable energy utilities, for example, and practices such as the deployment of anthrax. Another form of ecoterrorism, often referred to as environmental warfare, consists of the deliberate and illegal destruction, exploitation, or modification of the environment as a strategy of war or in times of armed conflict. Examples include the U.S. military's use of the defoliant Agent Orange during the Vietnam War and the destruction of Kuwaiti oil wells by retreating Iraqi military forces during the 1991 Persian Gulf War. The activities of some environmental activists also have been described as ecoterrorism. These activities include criminal trespass on the property of logging companies and other firms and obstruction of their operations through sabotage as well as the environmentally harmless modification of natural resources in order to make them unsuitable for commercial use (a practice known as “monkeywrenching”).

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