On June 30 two men drove a dark green Jeep Cherokee into a set of doors at the Glasgow airport in Scotland, producing a burst of flames that officials deemed an act of terrorism. They linked the crash to a broader plot that included two cars in London that contained explosive materials.

The foiled plan is just one of the tens of thousands of terrorist pursuits that have pockmarked the globe in recent decades--including the 1972 murder of 11 Israeli athletes at the Munich Olympics, the 1975 hostage taking at the OPEC headquarters in Vienna, the 1995 sarin gas attacks in Tokyo, and the September 11, 2001, strikes in the U.S. Although terrorism includes a diversity of actions, all of them, by definition, are intended to harm innocent civilians--and perpetrate fear--in the name of political, religious or other ideological goals.

Terrorism is an ageless scourge. But the ferocity of the 9/11 assaults and the upsurge in unrestrained activities by al-Qaeda and other groups have elicited heightened interest in unraveling the underpinnings of terrorism. Accompanying this brand of audacious intimidation is a new tactic for studying it--and perhaps curtailing it. Whereas earlier generations of researchers focused on the political roots of groups such as the Irish Republican Army (IRA), many of todays investigators are probing the minds of adherents to discover what drives them to carry out their demonic deeds.

Literature on this approach abounds. Amazon.com offers more than 800 books on "psychology and terrorism." According to the psychology database PsycInfo, more articles on terrorism have been published since 2001 than in the previous 120 years. Meanwhile the U.S. Department of Homeland Security has doled out $12 million to establish the Study of Terrorism and Responses to Terrorism (START), a research consortium of more than 30 scientists charged with investigating the origins, dynamics and psychological impacts of this devastating pursuit.

The latest research suggests, for example, that the vast majority of terrorists are not mentally ill but are essentially rational people who weigh the costs and benefits of terrorist acts, concluding that terrorism is profitable. The advantages accrued, however, have value only in a particular social context. Group dynamics, often driven by charismatic leadership, play a powerful role in convincing individuals to embrace expansive goals and use violence to attain them. Personal factors also draw people toward terror. Terrorist groups provide their members with a feeling of belonging and empowerment and, in some cases, a means of avenging past wrongs.

To be sure, many of the psychological explanations of terrorism rest on shaky ground, because empirical studies of the terrorist mind are relatively scarce, partly because of the difficulty in conducting them [see box on page 77]. "The number of suggested theories far outstrips the number of empirical studies in the literature," says psychiatry professor Jeff Victoroff of the University of Southern California. Nevertheless, researchers hope that the insights gained will help them thwart terrorism by dissolving the psychological glue that holds these rebel groups together.

Rise of Religion
Modern-day terrorism can be traced back as far as the first century A.D., when the Zealots of Judea secretly assassinated Roman occupation forces and collaborators because they felt that Roman rule was incompatible with Judaism. Like other religious extremists, the Zealots rejected the authority of a secular government and laws that did not incorporate their beliefs.

Centuries later the rise of nationalism engendered a new breed of terrorist, exemplified by the IRA, loyal to a collection of people who share the same culture and values. Most such nationalists aim to create or reclaim a homeland; their actions are designed to garner international sympathy for their cause and to coerce the dominant group to concede to their wishes. Social revolutionary terrorists such as the German Red Army Faction (RAF) and the Italian Red Brigades, on the other hand, seek to overthrow capitalism and the current social order.

During the 1970s and 1980s nationalists and social revolutionaries were responsible for most acts of terrorism. Both groups sought to influence the West and the establishment and consistently owned up to their deeds. But in recent decades no one has claimed responsibility for perhaps 40 percent of terrorist incidents, a fact experts attribute to the increasing frequency of terrorism perpetrated by religious extremists--modern terrorists in the tradition of the Zealots of Judea.

Unlike the more politically motivated factions, these religious terrorists do not seek influence per se but rather the destruction of the Western world in the name of God. (As such, attribution is superfluous. After all, God knows what happened.) This motive reveals why they are so dangerous: they are unconstrained by the negative Western political reaction, and instead of fearing death they embrace martyrdom. Thus, they are willing to spawn casualties with abandon, as demonstrated on September 11 and by the bombings of the U.S. embassies in Kenya and Tanzania in 1998 and the U.S.S. Cole in 2000.

The February 1998 fatwa issued by the World Islamic Front illustrates this destructive mind-set. It reads in part: "In compliance with Gods order, we issue the following fatwa to all Muslims: The ruling to kill the Americans and their allies--civilians and military--is an individual duty for every Muslim who can do it ... to liberate the al-Aqsa Mosque and the holy mosque (Mecca) from their grip, and in order for their armies to move out of all the lands of Islam, defeated and unable to threaten any Muslim."

Cool Operators
Such a mind-set may seem almost pathological. Indeed, many people reflexively brand terrorists as "crazy"; some researchers, too, have suspected psychiatric problems such as antisocial personality disorder as a cause of political or religious violence. Studies of members of the RAF in Germany, the IRA in Ireland and Hezbollah in Lebanon, among others, however, have yielded no evidence that terrorists are mentally ill.

Even suicide bombers are sane in most respects. After interviewing some 250 members of Hamas and Islamic Jihad in Gaza from 1996 to 1999, United Nations worker and journalist Nasra Hassan reported that none of these young would-be bombers struck her as depressive or despondent. They always discussed the attacks matter-of-factly and were motivated by deep religious feelings and the conviction that what they were doing was right.

An expert committee on the psychological causes of terrorism concluded in 2005 that individual psychopathology was insufficient to explain terrorism. In fact, terrorist leaders typically screen out such people from their organizations because their instability makes them dangerous. Instead many researchers now believe that, far from being lunatics, terrorists rationally calculate the costs and benefits of their actions. In this "rational choice" theory of terrorism, violence and the perpetration of fear make up an optimal strategy for achieving political and religious objectives.

Autobiographical tracts from terrorists such as Sean MacStiofain, the first chief of staff of the Provisional IRA, Palestine Liberation Organization activist Leila Khaled and the Brazilian guerrilla fighter Carlos Marighella support this view, according to terrorism expert Martha Crenshaw of Wesleyan University. These writings reveal that intellectualism can coexist with hatred and that political theorizing is a common outlet for frustration over political grievances. The theorizing becomes dangerous when it hardens into dogma.

Studies of the militant Islamist jihadists reveal similar signs of normalcy tucked inside fanaticism. After culling through government documents, media reports and court records on 400 of these extremists, forensic psychiatrist Marc Sageman of the University of Pennsylvania determined that these individuals are far from brainwashed, socially isolated, hopeless fighters. Ninety percent of them came from caring, intact families; 63 percent had gone to college, compared with the 5 to 6 percent background rate in the developing world, according to Sageman. Similarly, the suicide hijackers of 9/11 were well educated--three of them were in graduate school--and offspring of well-off Saudi and Egyptian families.

"These are the best and brightest of their societies in many ways," Sageman wrote in an essay about his 2004 book Understanding Terror Networks. "Terrorists are generally completely normal people.... People just like you and me."

Of course, not all terrorists come from financially and socially solid backgrounds. When Israeli social scientists conducted postmortem profiles of 93 Palestinian suicide bombers, aged 17 to 22, the scientists found that the bombers had been uniformly uneducated, unemployed and unmarried.

No matter their background, what seems to unite all terrorists is a willingness to subordinate their individual identity to a collective identity, according to political psychologist Jerrold M. Post of George Washington University. A growing number of researchers, including Post, believe terrorism can be best understood through the lens of group psychology. It is in that group context that terrorists rational calculus makes sense, as the benefits of terrorism are generally those of the group and not of the individual.

You Belong to Us
Charismatic leaders play an important role in setting these goals and convincing followers to embrace them. According to an article by Post in eJournal USA, Palestinian suicide bomb commanders have told their recruits: "You have a worthless life ahead of you, you can do something significant with your life, you will be enrolled in the hall of martyrs...." The bombers themselves then embrace the larger aims of their mission at great personal cost. When Massachusetts Institute of Technology graduate student Nichole Argo interviewed 15 Palestinians in Israeli prisons who had gone on failed suicide missions in 2003, she, too, found that they placed the interests of their society above their own welfare.

Osama bin Laden similarly convinced the 9/11 attackers to adopt his cause and subordinate their personal welfare to it. Like a religious cleric, bin Laden regularly referred to verses of the Quran to validate acts of extreme violence.

In Middle Eastern cultures, extremist political goals frequently are inculcated into young people very early in life. From interviews with 35 incarcerated Middle Eastern terrorists, Post and his colleagues learned that adults routinely teach children to hate the enemy, Israel, and to believe in the cause of defeating Israeli forces. One of the interviewees reported that he learned from the sheikh at his mosque how the enemy effectively evicted Palestinians from Palestine.

In interviews done by Posts team, militant Islamist terrorists from Hezbollah and Hamas justified suicide terrorism by terming it martyrdom, or self-sacrifice, in the name of Allah. Thus, such acts fulfilled another socially prescribed goal: they underscored the depth of a persons faith. Social context was critical to this idea. The researchers found that religiously motivated Islamist terrorists were more committed to self-sacrifice than were less religious perpetrators, whose objectives were purely political.

The Chechen rebels who held 800-odd Moscow theatergoers captive for 58 hours in October 2002 were equally committed to self-sacrifice for the supposed greater good. According to a 2004 study in which psychologist Anne Speckhard of the Free University of Brussels in Belgium interviewed 11 of the hostage survivors, the Chechen "freedom fighters" knew what they wanted: independence and an end to the harsh occupation of Chechnya.

At the same time, their religious beliefs motivated them to become martyrs for their cause. Nothing was more important to them than dying for their homeland. During the siege, one terrorist reportedly said, All of us have the same fate here. We are here to die. Terrorism was thus used as a means to fight back and to find personal meaning and justice where they were perceived as lacking.

Signing Up for Terror
Indeed, joining a radical group provides a sense of community, power and identity to people who might otherwise feel alone, powerless and unimportant. As one of the prisoners interviewed by Posts team declared: An armed action proclaims that "I am here, I exist, I am strong, I am in control ... I am on the map."

In some societies, social pressure comes into play. When asked why they joined, many of Posts interviewees responded that everyone was doing it and not to belong would mean ostracism. Psychologist John Horgan of Pennsylvania State University spoke to one ex-activist who had a similar explanation: "I just sort of slid into it; I had the feeling I was being sucked in by the group."

In addition to providing a sense of community and power, a terrorist organization can provide a means of vengeance for past humiliations. "What drives people to such acts of violence is a long history of humiliation and an overwhelming desire for revenge," opines Palestinian psychiatrist Eyad El-Sarraj, who directs the Gaza Community Mental Health Program. Many suicide bombers during the second intifada from 2000 to 2005, El-Sarraj says, had watched family members being killed, beaten and humiliated.

More than 70 percent of some 900 Muslim young people in the Gaza Strip interviewed by psychologist Brian K. Barber of the University of Tennessee had suffered severe trauma during the first intifada from 1987 to 1993. Many of these teenagers had been tear-gassed by Israeli soldiers or had experienced attacks while in school or at home. Studies of the backgrounds of other terrorists also indicate that trauma was the most important reason driving them into the underground movement.

In other cases, family strife may be a more significant factor. Criminologist Lorenz Boellinger of the University of Bremen in Germany and his colleagues probed the backgrounds of 250 people who had been suspected or convicted of terrorist activity--they read trial records and spoke to prison officers as well as to seven of the terrorists themselves. The researchers found that many of the activists had experienced stress early in life from poor family attachments or other social problems. The interviewees seemed to compensate for lifes disappointments and feelings of powerlessness by subscribing to a perturbed reality that was starkly defined by friends and enemies.

Turning the Tables
Terrorism is not just about violence, of course. As the name suggests, it is also about fear, as expressed in the Chinese maxim: "Kill one, frighten ten thousand." In many instances, this psychological tactic succeeds all too well: after 9/11, for example, the entire nation experienced high levels of psychological distress, studies have documented.

But now researchers hope to turn the tables on the terrorists. By probing the collective psyches of the terrorist groups themselves, they aim to find new ways to thwart the recruitment of additional group members, to inject dissention into terrorist societies, to facilitate escape from a terrorist life and perhaps to strip group leaders of their powers. By unraveling terrorist bonds, such tactics could eventually put a halt to many heinous crimes.