Terrorism, the systematic use of violence or threat of violence by organized groups to achieve specific goals, which may be political, religious, or ideological, to create fear. Several terrorists belong to revolutionary movements that seek to bring a change in the government or overthrowing the government to achieve liberation. Some seek to gain attention and support for certain political philosophies or religious ideas. Terrorist activities may be directed against individuals, organizations, or governments who are against their causes. Terrorists mostly abduct or kill business executives, diplomats, judges, police, and political leaders. Places of worship such as churches, mosques, synagogues, airplanes, buses, trains, and nightclubs are also attacked by terrorists. Methods used include murder, torture, kidnapping, hijacking, bombings, releasing harmful chemicals and biological substances and destruction of property. The newer methods include computer based terrorism and weapons of mass destruction. In a suicide bombing, a terrorist detonates explosives while wearing them in a public area, with the intent of killing the people nearby. The terrorist in suicide bombings takes away his own life while conducting the attack.

Assassinations or kidnappings of key government officials or other important individuals are directed at creating fear. Sometimes, terrorists also abduct people and hold them hostage until their demands are met. Tourists are also attacked by terrorists to discourage others from travel.

Hijackings of airplanes, buses, or other vehicles are also common terrorist methods. By using arms or bomb threats, terrorists seek to gain control. After gaining control, hijackers may take passengers as hostages and threaten to kill them if their demands are not met. On other instances, hijackers may threaten to blow up an airplane, or deliberately crash a plane into a target. Such hijackings are particularly dangerous because planes loaded with fuel can become flying bombs.

Biological attacks refer to deliberate spreading of harmful bacteria, viruses, and poisons. The use of biological agents to cause harm is known as germ warfare or bioterrorism. Bioterrorists seek to pollute food or water supplies, to distribute toxins, like ricin, or to spread harmful diseases like anthrax or smallpox. They can put harmful bacteria in restaurant salad bars or use the mail to send contaminated items. Such weapons however are difficult for terrorists to prepare and make use of effectively.

Chemical attacks involve intentional discharge of harmful chemicals. Some chemicals agents affect the nervous system and can lead to paralysis or even death. Others cause damage to the skin, eyes, nose, throat, or lungs. Some of the dangerous chemicals are mustard gas which causes burns and blindness; hydrogen cyanide which is sometimes used to execute criminals; and sarin which is a dangerous nerve gas. Terrorists may try to buy, steal, or produce chemical weapons and disperse them later in populated areas. Like the biological weapons, these weapons are also difficult for terrorists to prepare and use.

Nuclear attacks have never taken place because of the governments vigilance to keep the nuclear materials out of the reach of the terrorists. Counterterrorism experts however, have analyzed how in years to come terrorists might use the nuclear weapons or radioactive substances to carry out nuclear attacks.

It is feared that the terrorists might get hold of nuclear devices from an underground weapon supplier or from a government that possesses such devices. Terrorists might also try to acquire radioactive materials like weapons-grade plutonium or uranium to manufacture their own nuclear weapons. Also, if they are unable to get hold of the nuclear devices or the radioactive substances they might explode nuclear facilities. It is also feared that terrorists might pack radioactive substances with explosives to create radiological dispersion devices. Such devices, called dirty bombs could produce invisible radiation capable of causing sickness or death. The radioactive contamination could keep people away from an important area like a downtown business section for several months or years.

Computer-based terrorism or cyberterrorism refers to the disruption of computer information systems. Cyberterrorists may devise or circulate computer viruses to sabotage computer operations and destroy data. Cyberterrorists may also try to steal or change important information, or to attack systems that provide essential services.

Other forms of terrorism may include any other form of violence or threats of violence to cause panic. Some governments use terrorist methods like torture and murder to scare opposition and increase their authority. These violent methods used by the repressive governments are known as state terrorism or state-conducted terrorism. War crimes, genocide, or any other international violations may come under acts of terror.

Although individuals may conduct terrorist acts like bombings or distribution of computer viruses, terrorism is typically employed by organized networks or radical groups against established governments to obtain changes in policies, to force the release of imprisoned members of their organizations, or to gain the attention of the news media. Several groups may function within one nation or region. Others have divisions and operations in several countries. Guerilla warfare is a common tactic adopted by the terrorists who can not equal the strength of military forces. It includes attacks by roving groups of fighters who torment enemies with ambushes, bombings, unexpected raids, and other hit-and-run strategies. The fighters mingle with ordinary citizens, attack abruptly, and try to evade capture. They may try to paralyze the economy by demolishing bridges, dams, telephone networks, or other important structures or services. By doing so, they hope the general public would lose their sense of safety and their confidence in their government or establishment.

All terrorist acts are considered crimes under the international law. Many countries combat terrorism by obtaining information or intelligence, by beefing up security at airports, government offices, and other important buildings, and by cooperating with international organizations and other nations facing terror threats. Special military and law enforcement units are also prepared by some countries to take control of terror attacks. Actions designed to prevent terrorism are called counterterrorism. Terrorism is particularly effective for small groups with limited military and financial resources, such as ethnic minorities striving for independent states; for example, Tamil, Kurd, Chechen, Basque, and Palestinian organizations have used terrorism. There are however, some groups with international networks that conduct terror attacks in different parts of the world. Al-Qaida is one such large terror group which aims to endorse the goals of Islamic extremists. Religious fanatics of various faiths use terrorism. Ecoterrorists like the Earth Liberation Front and the Animal Liberation Front use terrorism against lumber companies and laboratories that conduct research on animals to protest the misuse of natural resources and wildlife. Terrorism is also used by criminals, particularly by organized criminal groups, to force cooperation, extort money, or prevent testimony against them.

A majority of the terrorist outfits are led by a leader or group of leaders who develop plans and direct operations. The plans are then carried out by active terrorists within the organization. Several terrorist organizations comprise of small units or cells. Terrorist cells may receive particular directions from leaders, or they may plan their own activities based on the organizations fundamental objectives. Terrorist groups always take great efforts to conceal the identities of their group members, location of their cells, and their modes of gathering information. Conventionally, only one member of each cell knows how to get in touch with the larger organization. Hence, the larger organization remains safe even if a cell is detected and destroyed. The confidentiality and intricacy of the cell structure makes it difficult for the governments to gain access to the terrorist groups.

The sources of funding for the terrorist groups are largely unknown. Some governments secretly provide aid in the form of weapons, training, and money to the terrorist groups. Money is also raised through criminal activities such as, theft or drug trafficking. In other instances, the terrorist groups use fake social service organizations to secure large donations from unaware donors.

Counterterrorism refers to a number of activities. Governments accumulate and analyze information about suspected terrorists and terrorist groups. They spot probable terrorist threats and develop a wide range of security measures and emergency procedures. A number of countries turn down any negotiation with terrorists or countries that support terrorists. United States Department of Homeland Security and the United Kingdoms Security Services (MI5) are the prominent national security services developed to counter terrorism. They get support from intelligence services, like Israels Mossad, the United Kingdoms Secret Intelligence Service (MI6), and the U.S. Central Intelligence Agency (CIA). International organizations such as the United Nations (UN) and Interpol assist nations to counter terrorism.

Any information related to terrorism is collected, shared, and examined by national governments, international organizations, police forces, and specialized intelligence services. Efforts like these help prevent attacks by recognizing terrorist suspects and by identifying terrorist plots while they are being designed.

Electronic surveillance is commonly used by several intelligence and law enforcement agencies to keep a watch on terrorists and to intercept their communication. The interception of telephone conversations by a listening machine connected to a telephone wire or placed nearby is called wiretapping. Special aircraft and artificial satellites are the other forms of surveillance that can produce detailed images of suspected terrorist bases.

Governments may work with agents from foreign countries or send undercover agents to gain more information from within a terrorist group. Also, by questioning the detained terrorists and by searching areas where terrorists have lived, governments can gather a lot of information. On some occasions, governments may also check the financial records and identify the sources of funding of terrorist groups. They may freeze the assets of terrorists or of individuals or groups suspected of providing funds to the terrorist organizations.

Most governments protect probable terrorist targets, such as airports, public gatherings, and government buildings by involving effective security systems and procedures as well as trained personal security. Tight security at airports and airplanes can help in avoiding hijacks and other terror attacks. Passengers often pass through multiple airport checkpoints. Guards search baggage and other items, and they may search passengers before letting them board the plane. Reinforced cockpit doors and armed air marshals are usually involved in security measures on the airplanes.

Skyscrapers, government buildings, and several other structures have physical barriers to keep cars or trucks from getting closer. A number of buildings also have metal detractors or security checkpoints to detect dangerous materials and to stop unauthorized people from entering. Cameras are installed at crowded places to scan peoples faces and attempt to match them with photos of suspected terrorists.

Cyberterrorism can be tackled with the help of security measures such as antivirus programs and electronic barriers called firewalls. New technology would evolve with time to counter cyberterrorism more effectively. One of the essential aspects of cyberterrorism is protection of important sites. In some cases however, target hardening may cause target displacement which may cause the terrorists to transfer their plans to other soft targets that are not properly protected.

One of the chief ways by which terrorism can be countered is through cooperation between organizations and governments. The UN and other international agencies assist in the promotion of this cooperation. A number of treaties and agreements have been in place to control terrorism. The extradition treaties, for instance, allow people linked to terrorism in one country to be arrested in another country and deported back for trial. Such treaties have made it difficult for the terrorists to escape.

The international community may isolate or punish countries, which provide support to terrorism. Economic sanctions could be imposed on such countries until they change their policy on terrorism. In case sanctions and diplomatic pressure fail, military attacks on terror camps may also be launched. A governments ability to fight terrorism depends on a large extent to its ability to cut off communication to and from suspected terrorists, to search individuals for arms and other dangerous materials, and to inspect and arrest suspects. Such actions, may conflict with the basic rights and freedoms in a democracy. The governments today face a stiff challenge in countering terrorism while protecting the civil rights and privacy of individuals. Government officials, legal experts, and civil rights activities debate on the best way to deal with these two interests.

History of terrorism traces back to the spread of early civilization. Since ancient times, individuals, rebel factions, and governments have used violence and force to kill enemies, to spread fear, and to achieve political, religious, and other goals. Early terrorism began when the empire builders asserted control over the conquered people by force. In 71 B.C, the Roman general Crassus crushed a rebellion by the gladiator Spartacus. The rebels were then publicly crucified to warn others the result of rebellion. Terrorist methods were used by some groups against their rulers, as it happened in the case of the Jewish group, Sicarii which waged wars against the Romans from A.D. 6 to 73.

In the 9th century, Japanese ninja, members of an underground organization of peasant families, spread terror through the means of destruction, assassination, and abduction. Ninja were experts in various armed and unarmed combats, including the use of disguises and poisons. In the 12th century, Persia (now Iran) and Asia Minor (now part of Turkey) witnessed violent campaigns carried out by a secret society named assassins (or hashshashin or hemp-eaters). They smoked hashish, a drug, made from the hemp plant and killed their enemies while under its influence. In the 14th and 15th centuries, Europe experienced violent peasant uprisings that can now be called terrorist in nature.

Modern terrorism evolved after the word terrorism made its first appearance during the French Revolution (1789-1799). The policy of violence against enemies was followed by some of the revolutionaries. Around 40,000 people were executed by the revolutionaries. The number of executions and fears of getting killed created a sense of panic among all. This led to the period being known as the Reign of Terror. By the early 19th century, terrorism had become a clash of rebellion and conflict across the world.

In the early 20th century, terrorist strategies came to be used quite widely by the dictators Adolf Hitler of Germany, Benito Mussolini of Italy, and Joseph Stalin of Soviet Union. In the late 20th century, General Augusto Pinochet Ugarte took over Chile as an army dictator. Under his rule, over 3,000 Chileans disappeared or were killed, and several others tortured. A number of authoritarian governments still use state terrorism to terrorize and control the population.

Terrorist groups and movements have used violence to achieve their goals. The Ku Klux Klan, an American group, has used terrorism to oppose the progression of African Americans, Jews, and other minorities since the late 19th century. Roman Catholics in Northern Ireland have used terrorism to put an end to British rule and to unite Northern Ireland with the Republic of Ireland. Simultaneously, the Protestant extremists have used terrorism to demand for the continuation of the British rule.

The demand for an independent Basque state in Spain saw the emergence of a group named Euskadi ta Askatasuna (Basque Homeland and Freedom), abbreviated ETA, which used violence to meet its demand. In Chechnya, rebels have taken up terrorism to gain independence from Russia. The rebel groups have taken hostages and carried out suicide bombings against Russian targets.

A Jewish group, Irgun Zvai Leumi (National Military Organization) used violence to accelerate the end of the British rule in Palestine and create a Jewish homeland before Israel gained independence in 1948. Since 1960, Palestinian groups like Hamas and Islamic Jihad of Palestine have conducted several campaigns of terrorism aimed at creating an independent Palestinian state. They have carried out a series of suicide bombings in the early 21st century against Israel. Israel in response has conducted several military strikes that have claimed civilian lives.

During the late 20th century, a number of terrorist groups worked for the destruction of the political and economic systems in their homelands and the development of new political systems. Among these were the Red Brigades in Italy and the Red Army faction or the Baader-Meinhof Gang in West Germany. Since the late 20th century, Peru has witnessed attacks by Leftist terrorist groups called Shining Path and the Tupac Amaru Revolutionary Movement.

A number of terrorist attacks have religious motives rather than political ones. In 1995, 12 people were killed and thousands injured when the members of a Japanese religious cult released the nerve gas sarin into the Tokyo Subway system. In the U.S. and other nations, clinics have been bombed and doctors performing abortions murdered by those who opposed abortions. People who oppose abortions usually do so because of religious beliefs. In the late 20th century, several terrorist groups began forming networks on an increasingly global scale. Some of these groups, especially in the Middle East, held a deep hatred for the U.S. and other western countries. Fears of the terrorists in possession of weapons of mass destruction also rose drastically.