Legal statutes in most countries around the world regard terrorism as a crime. Yet there is considerable variation in how these laws define terrorism, even in countries whose laws derive from a common origin.

In the United Kingdom, for example, legislation titled Terrorist Act 2000 states that terrorism is “the use or threat of action . . . designed to influence the government or to intimidate the public or a section of the public . . . for the purpose of advancing a political, religious or ideological cause.” The legal system and code of law of the United Kingdom has influenced those of the United States, Canada, and Israel.

United States federal statute defines terrorism as “violent acts or acts dangerous to human life that . . . 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 assassination or kidnapping.” This definition appears in United States Code, Title 18, Section 2331 (18 USC 2331).

Canada's Anti-terrorism Act (Bill C-36) designates “terrorist activity” as “an act or omission . . . that is committed in whole or in part for a political, religious or ideological purpose, objective or cause and in whole or in part with the intention of intimidating the public, or a segment of the public, with regard to its security, including its economic security, or compelling a person, a government or a domestic or an international organization to do or to refrain from doing any act, whether the person, government or organization is inside or outside Canada . . . .”

Israeli law does not address terrorism specifically. But in the Prevention of Terrorism Ordinance No. 33, it defines a terrorist organization as “a body of persons resorting in its activities to acts of violence calculated to cause death or injury to a person or to threats of such acts of violence.”

III Causes of terrorism

Terrorism has occurred throughout history for a variety of reasons. Its causes can be historical, cultural, political, social, psychological, economic, or religious—or any combination of these. Some countries have proven to be particularly susceptible to terrorism at certain times, as Italy and West Germany were during the 1970s. Terrorist violence escalated precipitously in those two countries for a decade before declining equally dramatically. Other countries, such as Canada and The Netherlands, have proven to be more resistant, and have experienced only a few isolated terrorist incidents.

In general, democratic countries have provided more fertile ground for terrorism because of the open nature of their societies. In such societies citizens have fundamental rights, civil liberties are legally protected, and government control and constant surveillance of its citizens and their activities is absent. By the same token, repressive societies, in which the government closely monitors citizens and restricts their speech and movement, have often provided more difficult environments for terrorists. But even police states have not been immune to terrorism, despite limiting civil liberties and forbidding free speech and rights of assembly. Examples include Russia under tsarist rule and the Communist-ruled Union of Soviet Socialist Republics, as well as the People's Republic of China, Myanmar, and Laos.

In broad terms the causes that have commonly compelled people to engage in terrorism are grievances borne of political oppression, cultural domination, economic exploitation, ethnic discrimination, and religious persecution. Perceived inequities in the distribution of wealth and political power have led some terrorists to attempt to overthrow democratically elected governments. To achieve a fairer society, they would replace these governments with socialist or communist regimes. Left-wing terrorist groups of the 1960s and 1970s with such aims included Germany's Baader-Meinhof Gang, Italy's Red Brigades, and the Weather Underground (see Weathermen) in the United States. Other terrorists have sought to fulfill some mission that they believe to be divinely inspired or millennialist (related to the end of the world). (See Millennium). The Japanese religious cult Aum Shinrikyo, responsible for a nerve gas attack on the Tokyo subway in 1995 that killed 12 people, falls into this category. Still other terrorists have embraced comparatively more defined and comprehensible goals such as the re-establishment of a national homeland (for example, Basque separatists in Spain) or the unification of a divided nation (Irish nationalists in Northern Ireland).

Finally, some terrorists are motivated by very specific issues, such as opposition to legalized abortion or nuclear energy, or the championing of environmental concerns (see Environment) and animal rights. They hope to pressure both the public and its representatives in government to enact legislation directly reflecting their particular concern. Militant animal rights activists, for example, have used violence against scientists and laboratory technicians in their campaign to halt medical experimentation involving animals. Radical environmentalists have sabotaged logging operations and the construction of power grids to protest the spoiling of natural wilderness areas. Extremists who oppose legalized abortion in the United States have attacked clinics and murdered doctors and other employees in hopes of denying women the right to abortion.

National governments have at times aided terrorists to further their own foreign policy goals. So-called state-sponsored terrorism, however, falls into a different category altogether. State-sponsored terrorism is a form of covert (secret) warfare, a means to wage war secretly through the use of terrorist surrogates (stand-ins) as hired guns. The U.S. Department of State designates countries as state sponsors of terrorism if they actively assist or aid terrorists, and also if they harbor past terrorists or refuse to renounce terrorism as an instrument of policy.

State sponsorship has proven invaluable to some terrorist organizations—by supplying arms, money, and a safe haven, among other things. In doing so, it has transformed ordinary groups, with otherwise limited capabilities, into more powerful and menacing opponents. State sponsorship can also place at terrorists' disposal the resources of an established country's diplomatic, military, and intelligence services. These services improve the training of terrorists and facilitate planning and operations. Finally, governments have paid terrorists handsomely for their services. They thereby turn weak and financially impoverished groups into formidable, well-endowed terrorist organizations with an ability to attract recruits and sustain their struggle.

The U.S. Department of State has designated seven countries as state sponsors of terrorism: Iran, Iraq, Syria, Libya, Cuba, North Korea, and Sudan. In the year 2000, it named Iran as the most active supporter of terrorism for aid to groups such as Hezbollah, Hamas, and Palestine Islamic Jihad. Although the former Taliban government in Afghanistan sponsored al-Qaeda, the radical group led by Saudi exile Osama bin Laden, the United States did not recognize the Taliban as a legitimate government and thus did not list it as a state sponsor of terrorism.