What exactly is terrorism? A terrorist act would appear to be easily recognizable. Despite laws and international treaties defining terrorism as criminal behavior, many people have their own perceptions as to what constitutes terrorism.

The pattern is familiar. First, a bomb attack or other violent act takes place. Then, frequently, a so-called "communiqué" is issued by some group claiming responsibility for the attack. Meanwhile, authorities and the society at large deal with the impact -- death and destruction.

The Sari Club in Bali, bombed in 2002

Terrorism can occur anywhere, and it usually comes in the form of a surprise attack. In Samarra, Iraq, a Shi'a shrine was blasted into ruins in February. On the Indonesian island of Bali, three suicide bombers took 20 lives last October. In London, bombs ripped apart three subway stations and a bus last July. And in the United States, on September 11, 2001, hijacked airliners toppled New York City's World Trade Center and slammed into the Pentagon near Washington.

Violence Linked by a Common Goal

Analyst Brian Jackson, with the RAND Corporation in Washington, says that while the goals of specific terrorist groups may vary, there is a common thread linking these acts of violence.  He says, "Terrorism is a psychological weapon. It's attempting to cause fear, and, through causing that fear, influence others. So by injuring some members of the population, you attempt to cause fear across that population and, by doing that, have that population exert pressure on the government to change its decisions."

Terror and a Change in Government

That is exactly what happened in Spain two years ago. Three days before national

The commuter train bombings in Madrid changed how people voted

elections, a series of explosions ripped apart four commuter trains, killing about 200 people. Conservative Prime Minister Jose Maria Aznar, who had sent troops to join the U.S.-led coalition in Iraq, blamed the Basque separatist group ETA for the bombings. Then, al-Qaida claimed responsibility for the blasts and demanded that Spain withdraw its troops from Iraq. Spanish voters responded by electing the opposition Socialist Party of Jose Luis Rodriguez Zapatero. One of Mr. Zapatero's first acts as Spain's leader was to pull Spanish forces out of Iraq.

A Broadview and the Legal Perspective

At the Center for Defense Information in Washington, analyst Steven Welsh says there is a broadly accepted view of what constitutes terrorism.

According to Mr. Welsh, "Traditional definitions usually include the use of violence in order to intimidate a civilian population or to coerce a government, usually carried out by non-state actors or clandestine agents who do not have a lawful basis, in order to disrupt otherwise peaceful settings or the conduct of national affairs."

Although most experts on the subject say terrorism is a political term rather than a legal one, nations and international treaties have sought to put terrorist-related crimes like aircraft hijacking and the murder of diplomats into a legal context. But these definitions can vary in scope and content.

Jeffrey Breinholt is Deputy Chief for Counterterrorism at the U.S. Department of Justice.  He says, "There is no such thing in the United States as a 'crime of terrorism.' Instead, what we do as a government is to list those things that we know terrorists do from our experience with them, and then make it a crime to commit those various acts."

Unlawful possession of weapons and explosives and destruction of U.S. government property are some of the terrorism-connected acts covered by U.S. federal law.

The Influence of Perceptions

Regardless of how terrorism is defined, Brent Heminger at the independent Terrorism Research Center in Washington says there are people who do not see specific acts as terrorism because of their own political or social beliefs.

Mr. Heminger contends, "If you went out in the streets in the U.S. and asked 10 separate Americans of all nationalities and creeds what terrorism is, you would get 10 different answers. Each person's perception of a terrorism fighter and a 'freedom fighter' is different, especially in the U.S. In the 1980s, terrorists in Central America were, in fact, our 'freedom fighters.'"

Some people have defended the Irish Republican Army's violence in Northern Ireland as part of a legitimate effort to unite the British-ruled region with the Irish Republic. Similar justifications have been made regarding violence by Chechen and Sri Lankan separatists.

Perceptions of terrorism can also be shaped by religion. Some people claim that the holy writings of their faith contain passages that provide justification for violence -- this, despite the fact that all major religions say the killing of innocent people is unacceptable.

Violence Rises to Maintain Terror's Shock Value

New York's World Trade Center, September 11, 2001

The death toll from a single act of terrorism soared to new heights with the murder of roughly 3 thousand people in the September 11, 2001 attacks on New York and Washington. To RAND Corporation analyst Brian Jackson, terrorism's mounting bloodshed reflects the perpetrators' attempts to always make the greatest possible impact with their crimes.

"In the 1970s and 1980s, terrorism was frequently a case where the group tried to kill a few to scare many for whatever reason," says Mr. Jackson. "As societies have gradually become more accustomed to violence, as we see groups with different goals, we've seen terrorist organizations that have really scaled up their activities to try to kill more people."

Fighting Terrorism

The West views terrorism as a significant threat to peace and stability that compels strong and comprehensive action. Center for Defense Information analyst Steven Welsh says efforts to combat such violence have to go far beyond the apprehension and punishment of those who perpetrate violence.

Mr. Welsh contends, "In order to cast the broad net, to get everybody who shares the guilt and to look at things we need to put a stop to in order to prevent terrorism, we need to look at the ancillary activities that radiate out from the violent act itself -- such as the financing, the planning and the incitement to violence."

Those activities, aided by modern technologies to allow surreptitious movement and communications, make the global war against terrorists increasingly complex and difficult. But the United States and other nations say they will not be deterred in their effort to defeat them.

In our next report on terrorism, we'll explore the socio-economic, religious and political factors that motivate terrorists.