Terrorism is a peculiar category of violence, because it has a cockeyed ratio of fear to harm. Compared to the number of deaths from homicide, war, and genocide, the worldwide toll from terrorism is in the noise: fewer than 400 deaths a year since 1968 from international terrorism (where perpetrators from one country cause damage in another), and about 2,500 a year since 1998 from domestic terrorism. The numbers we have been dealing with in this chapter have been at least two orders of magnitude higher.

But after the September 11, 2001, attacks, terrorism became an obsession. Pundits and politicians turned up the rhetoric to eleven, and the word existential (generally modifying threat or crisis) had not seen as much use since the heyday of Sartre and Camus. Experts proclaimed that terrorism made the United States "vulnerable" and "fragile," and that it threatened to do away with the "ascendancy of the modern state," "our way of life," or "civilization itself." In a 2005 essay in The Atlantic, for example, a former White House counterterrorism official confidently prophesied that by the tenth anniversary of the 9/11 attacks the American economy would be shut down by chronic bombings of casinos, subways, and shopping malls, the regular downing of commercial airliners by shoulder-launched missiles, and acts of cataclysmic sabotage at chemical plants. The massive bureaucracy of the Department of Homeland Security was created overnight to reassure the nation with such security theater as color-coded terrorist alerts, advisories to stock up on plastic sheeting and duct tape, obsessive checking of identification cards (despite fakes being so plentiful that George W. Bush's own daughter was arrested for using one to order a margarita), the confiscation of nail clippers at airports, the girding of rural post offices with concrete barriers, and the designation of eighty thousand locations as "potential terrorist targets," including Weeki Wachee Springs, a Florida tourist trap in which comely women dressed as mermaids swim around in large glass tanks.

All this was in response to a threat that has killed a trifling number of Americans. The nearly 3,000 deaths from the 9/11 attacks were literally off the chart -- way down in the tail of the power-law distribution into which terrorist attacks fall. According to the Global Terrorism Database of the National Consortium for the Study of Terrorism and Responses to Terrorism (the major publicly available dataset on terrorist attacks), between 1970 and 2007 only one other terrorist attack in the entire world has killed as many as 500 people. In the United States, Timothy McVeigh's bombing of a federal office building in Oklahoma City in 1995 killed 165, a shooting spree by two teenagers at Columbine High School in 1999 killed 17, and no other attack has killed as many as a dozen. Other than 9/11, the number of people killed by terrorists on American soil during these thirty-eight years was 340, and the number killed after 9/11-- the date that inaugurated the so-called Age of Terror -- was 11. While some additional plots were foiled by the Department of Homeland Security, many of their claims have turned out to be the proverbial elephant repellent, with every elephant-free day serving as proof of its effectiveness.

Compare the American death toll, with or without 9/11, to other preventable causes of death. Every year more than 40,000 Americans are killed in traffic accidents, 20,000 in falls, 18,000 in homicides, 3,000 by drowning (including 300 in bathtubs), 3,000 in fires, 24,000 from accidental poisoning, 2,500 from complications of surgery, 300 from suffocation in bed, 300 from inhalation of gastric contents, and 17,000 by "other and unspecified nontransport accidents and their sequelae." In fact, in every year but 1995 and 2001, more Americans were killed by lightning, deer, peanut allergies, bee stings, and "ignition or melting of nightwear" than by terrorist attacks. The number of deaths from terrorist attacks is so small that even minor measures to avoid them can increase the risk of dying. The cognitive psychologist Gerd Gigerenzer has estimated that in the year after the 9/11 attacks, 1,500 Americans died in car accidents because they chose to drive rather than fly to their destinations out of fear of dying in a hijacked or sabotaged plane, unaware that the risk of death in a plane flight from Boston to Los Angeles is the same as the risk of death in a car trip of twelve miles. In other words the number of people who died by avoiding air travel was six times the number of people who died in the airplanes on September 11. And of course the 9/11 attacks sent the United States into two wars that have taken far more American and British lives than the hijackers did, to say nothing of the lives of Afghans and Iraqis.

The discrepancy between the panic generated by terrorism and the deaths generated by terrorism is no accident. Panic is the whole point of terrorism, as the word itself makes clear. Though definitions vary (as in the cliché "One man's terrorist is another man's freedom fighter"), terrorism is generally understood as premeditated violence perpetrated by a nonstate actor against noncombatants (civilians or off-duty soldiers) in pursuit of a political, religious, or social goal, designed to coerce a government or to intimidate or convey a message to a larger audience. The terrorists may want to extort a government into capitulating to a demand, to sap people's confidence in their government's ability to protect them, or to provoke massive repression that will turn people against their government or bring about violent chaos in which the terrorist faction hopes to prevail. Terrorists are altruistic in the sense of being motivated by a cause rather than by personal profit. They act by surprise and in secrecy; hence the ubiquitous appellation "cowardly." And they are communicators, seeking publicity and attention, which they manufacture through fear.

Terrorism is a form of asymmetrical warfare -- a tactic of the weak against the strong -- which leverages the psychology of fear to create emotional damage that is disproportionate to its damage in lives or property. Cognitive psychologists such as Tversky, Kahneman, Gigerenzer, and Slovic have shown that the perceived danger of a risk depends on two mental hobgoblins. The first is fathomability: it's better to deal with the devil you know than the devil you don't. People are nervous about risks that are novel, undetectable, delayed in their effects, and poorly understood by the science of the day. The second contributor is dread. People worry about worst-case scenarios, the ones that are uncontrollable, catastrophic, involuntary, and inequitable (the people exposed to the risk are not the ones who benefit from it). The psychologists suggest that the illusions are a legacy of ancient brain circuitry that evolved to protect us against natural risks such as predators, poisons, enemies, and storms. They may have been the best guide to allocating vigilance in the prenumerate societies that predominated in human life until the compilation of statistical databases within the past century. Also, in an era of scientific ignorance these apparent quirks in the psychology of danger may have brought a secondary benefit: people exaggerate threats from enemies to extort compensation from them, to recruit allies against them, or to justify wiping them out preemptively (the superstitious killing discussed in chapter 4).

Fallacies in risk perception are known to distort public policy. Money and laws have been directed at keeping additives out of food and chemical residues out of water supplies which pose infinitesimal risks to health, while measures that demonstrably save lives, such as enforcing lower highway speeds, are resisted. Sometimes a highly publicized accident becomes a prophetic allegory, an ominous portent of an apocalyptic danger. The 1979 accident at the Three Mile Island nuclear power plant killed no one, and probably had no effect on cancer rates, but it halted the development of nuclear power in the United States and thus will contribute to global warming from the burning of fossil fuels for the foreseeable future.

The 9/11 attacks also took on a portentous role in the nation's consciousness. Large-scale terrorist plots were novel, undetectable, catastrophic (compared to what had come before), and inequitable, and thus maximized both unfathomability and dread. The terrorists' ability to gain a large psychological payoff for a small investment in damage was lost on the Department of Homeland Security, which outdid itself in stoking fear and dread, beginning with a mission statement that warned, "Today's terrorists can strike at any place, at any time, and with virtually any weapon." The payoff was not lost on Osama bin Laden, who gloated that "America is full of fear from its north to its south, from its west to its east," and that the $500,000 he spent on the 9/11 attacks cost the country more than half a trillion dollars in economic losses in the immediate aftermath.

The ups and downs of terrorism, then, are a critical part of the history of violence, not because of its toll in deaths but because of its impact on a society through the psychology of fear. In the future, of course, terrorism really could have a catastrophic death toll if the hypothetical possibility of an attack with nuclear weapons ever becomes a reality. I will discuss nuclear terrorism in the next section but for now will stick to forms of violence that have actually taken place.

Responsible leaders occasionally grasp the arithmetic of terrorism. In an unguarded moment during the 2004 presidential campaign, John Kerry told a New York Times interviewer, "We have to get back to the place we were, where terrorists are not the focus of our lives, but they're a nuisance. As a former law-enforcement person, I know we're never going to end prostitution. We're never going to end illegal gambling. But we're going to reduce it, organized crime, to a level where it isn't on the rise. It isn't threatening people's lives every day, and fundamentally, it's something that you continue to fight, but it's not threatening the fabric of your life." Confirming the definition of a gaffe in Washington as "something a politician says that is true," George Bush and Dick Cheney pounced on the remark, calling Kerry "unfit to lead," and he quickly backpedaled.

Terrorism is not new. After the Roman conquest of Judea two millennia ago, a group of resistance fighters furtively stabbed Roman officials and the Jews who collaborated with them, hoping to force the Romans out. In the 11th century a sect of Shia Muslims perfected an early form of suicide terrorism by getting close to leaders who they thought had strayed from the faith and stabbing them in public, knowing they would immediately be slain by the leader's bodyguards. From the 17th to the 19th century, a cult in India strangled tens of thousands of travelers as a sacrifice to the goddess Kali. These groups did not accomplish any political change, but they left a legacy in their names: the Zealots, the Assassins, and the Thugs. And if you associate the word anarchist with a black-clad bomb-thrower, you are recalling a movement around the turn of the 20th century that practiced "propaganda of the deed" by bombing cafés, parliaments, consulates, and banks and by assassinating dozens of political leaders, including Czar Alexander II of Russia, President Sadi Carnot of France, King Umberto I of Italy, and President William McKinley of the United States. The durability of these eponyms and images is a sign of the power of terrorism to lodge in cultural consciousness.

Anyone who thinks that terrorism is a phenomenon of the new millennium has a short memory. The romantic political violence of the 1960s and 1970s included hundreds of bombings, hijackings, and shootings by various armies, leagues, coalitions, brigades, factions, and fronts. The United States had the Black Liberation Army, the Jewish Defense League, the Weather Underground (who took their name from Bob Dylan's lyric "You don't need a weatherman to know which way the wind blows'), the FALN (a Puerto Rican independence group), and of course the Symbionese Liberation Army. The SLA contributed one of the more surreal episodes of the 1970s when they kidnapped newspaper heiress Patty Hearst in 1974 and brainwashed her into joining the group, whereupon she adopted "Tanya" as her nom de guerre, helped them rob a bank, and posed for a photograph in a battle stance with beret and machine gun in front of their seven-headed cobra flag, leaving us one of the iconic images of the decade (together with Richard Nixon's victory salute from the helicopter that would whisk him from the White House for the last time, and the blow-dried Bee Gees in white polyester disco suits).

Europe, during this era, had the Provisional Irish Republican Army and the Ulster Freedom Fighters in the U. K., the Red Brigades in Italy, the Baader-Meinhof Gang in Germany, and the ETA (a Basque separatist group) in Spain, while Japan had the Japanese Red Army and Canada had the Front de Libération du Québec. Terrorism was so much a backdrop to European life that it served as a running joke in Luis Buñuel's 1977 love story That Obscure Object of Desire, in which cars and stores blow up at random and the characters barely notice.

Where are they now? In most of the developed world, domestic terrorism has gone the way of the polyester disco suits. It's a little-known fact that most terrorist groups fail, and that all of them die. Lest this seem hard to believe, just reflect on the world around you. Israel continues to exist, Northern Ireland is still a part of the United Kingdom, and Kashmir is a part of India. There are no sovereign states in Kurdistan, Palestine, Quebec, Puerto Rico, Chechnya, Corsica, Tamil Eelam, or Basque Country. The Philippines, Algeria, Egypt, and Uzbekistan are not Islamist theocracies; nor have Japan, the United States, Europe, and Latin America become religious, Marxist, anarchist, or new-age utopias.

The numbers confirm the impressions. In his 2006 article "Why Terrorism Does Not Work," the political scientist Max Abrahms examined the twenty-eight groups designated by the U. S. State Department as foreign terrorist organizations in 2001, most of which had been active for several decades. Putting aside purely tactical victories (such as media attention, new supporters, freed prisoners, and ransom), he found that only 3 of them (7 percent) had attained their goals: Hezbollah expelled multinational peacekeepers and Israeli forces from southern Lebanon in 1984 and 2000, and the Tamil Tigers won control over the northeastern coast of Sri Lanka in 1990. Even that victory was reversed by Sri Lanka's rout of the Tigers in 2009, leaving the terrorist success rate at 2 for 42, less than 5 percent. The success rate is well below that of other forms of political pressure such as economic sanctions, which work about a third of the time. Reviewing its recent history, Abrahms noted that terrorism occasionally succeeds when it has limited territorial goals, like evicting a foreign power from land it had gotten tired of occupying, such as the European powers who in the 1950s and 1960s withdrew from their colonies en masse, terrorism or no terrorism. But it never attains maximalist goals such as imposing an ideology on a state or annihilating it outright. Abrahms also found that the few successes came from campaigns in which the groups targeted military forces rather than civilians and thus were closer to being guerrillas than pure terrorists. Campaigns that primarily targeted civilians always failed.

Nor do they get what they want. No small terrorist organization has ever taken over a state, and 94 percent fail to achieve any of their strategic aims. Terrorist campaigns meet their end when their leaders are killed or captured, when they are rooted out by states, and when they morph into guerrilla or political movements. Many burn out through internal squabbling, a failure of the founders to replace themselves, and the defection of young firebrands to the pleasures of civilian and family life.

Terrorist groups immolate themselves in another way. As they become frustrated by their lack of progress and their audiences start to get bored, they escalate their tactics. They start to target victims who are more newsworthy because they are famous, respected, or simply numerous. That certainly gets people's attention, but not in the way the terrorists intend. Supporters are repulsed by the "senseless violence" and withdraw their money, their safe havens, and their reluctance to cooperate with the police. The Red Brigades in Italy, for example, self-destructed in 1978 when they kidnapped the beloved former prime minister Aldo Moro, kept him in captivity for two months, shot him eleven times, and left his body in the trunk of a car. Earlier the FLQ overplayed its hand during the October Crisis of 1970 when it kidnapped Québec labor minister Pierre Laporte and strangled him with his rosary, also leaving his body in a trunk. McVeigh's killing of 165 people (including 19 children) in the bombing of a federal building in Oklahoma City in 1995 took the stuffing out of the right-wing antigovernment militia movement in the United States. As Cronin puts it, "Violence has an international language, but so does decency."

In her book How Terrorism Ends, the political scientist Audrey Cronin examined a larger dataset: 457 terrorist campaigns that had been active since 1968. Like Abrahms, she found that terrorism virtually never works. Terrorist groups die off exponentially over time, lasting, on average, between five and nine years. Cronin points out that "states have a degree of immortality in the international system; groups do not."

Attacks on civilians can doom terrorists not just by alienating potential sympathizers but by galvanizing the public into supporting an all-out crackdown. Abrahms tracked public opinion during terrorist campaigns in Israel, Russia, and the United States and found that after a major attack on civilians, attitudes toward the group lurched downward. Any willingness to compromise with the group or to recognize the legitimacy of their grievance evaporated. The public now believed that the terrorists were an existential threat and supported measures that would snuff them out for good. The thing about asymmetric warfare is that one side, by definition, is a lot more powerful than the other. And as the saying goes, the race may not be given to the swift, nor the battle to the strong, but that's the way to bet.

Though terrorist campaigns have a natural arc that bends toward failure, new campaigns can spring up as quickly as old ones fizzle. The world contains an unlimited number of grievances, and as long as the perception that terrorism works stays ahead of the reality, the terrorist meme may continue to infect the aggrieved.

The historical trajectory of terrorism is elusive. Statistics begin only around 1970, when a few agencies began to collect them, and they differ in their recording criteria and their coverage. It can be hard, even in the best of times, to distinguish terrorist attacks from accidents, homicides, and disgruntled individuals going postal, and in war zones the line between terrorism and insurgency can be fuzzy. The statistics are also heavily politicized: various constituencies may try to make the numbers look big, to sow fear of terrorism, or small, to trumpet their success in fighting terrorism. And while the whole world cares about international terrorism, governments often treat domestic terrorism, which kills six to seven times as many people, as no one else's business. The most comprehensive public dataset we have is the Global Terrorism Database, an amalgamation of many of the earlier datasets. Though we can't interpret every zig or zag in the graphs at face value, because some may represent seams and overlaps between databases with different coding criteria, we can try to get a general sense of whether terrorism really has increased in the so-called Age of Terror.

The safest records are those for terrorist attacks on American soil, if for no other reason than that there are so few of them that each can be scrutinized. Figure 6-9 shows all of them since 1970, plotted on a logarithmic scale because otherwise the line would be a towering spike for 9/11 poking through a barely wrinkled carpet. With the lower altitudes stretched out by the logarithmic scale, we can discern peaks for Oklahoma City in 1995 and Columbine in 1999 (which is a dubious example of "terrorism," but with a single exception, noted below, I never second-guess the datasets when plotting the graphs). Apart from this trio of spikes, the trend since 1970 is, if anything, more downward than upward.

FIGURE 6-9: Rate of deaths from terrorism, United States, 1970-2007

Source: Global Terrorism Database, START (National Consortium for the Study of Terrorism and Responses to Terrorism, 2010, http://www. start. umd. edu/gtd/), accessed on April 6, 2010. The figure for 1993 was taken from the appendix to National Consortium for the Study of Terrorism and Responses to Terrorism, 2009. Since the log of 0 is undefined, years with no deaths are plotted at the arbitrary value 0.0001.

What about the world as a whole? Though Bush administration statistics released in 2007 seemed to support their warnings about a global increase in terrorism, the HSRP team noticed that their data include civilian deaths from the wars in Iraq and Afghanistan, which would be classified as civil war casualties if they had taken place anywhere else in the world. The picture is different when the criteria are kept consistent and these deaths are excluded. Figure 6-11 shows the worldwide annual rate of death from terrorism (as usual, per 100,000 population) without these deaths. The death tolls for the world as a whole have to be interpreted with caution, because they come from a hybrid dataset and can float up and down with differences in how many news sources were consulted in each of the contributing datasets. But the shapes of the curves turn out to be the same when they include only the larger terrorist events (those with death tolls of at least twenty-five), which are so newsworthy that they are likely to have been included in all the subdatasets.

The trajectory of terrorism in Western Europe (figure 6-10) illustrates the point that most terrorist organizations fail and all of them die. Even the spike from the 2004 Madrid train bombings cannot hide the decline from the glory years of the Red Brigades and the Baader-Meinhof Gang.

Source: Global Terrorism Database, START (National Consortium for the Study of Terrorism and Responses to Terrorism, 2010, http://www. start. umd. edu/gtd/), accessed on April 6, 2010. Data for 1993 are interpolated. Population figures from UN World Population Prospects (United Nations, 2008), accessed April 23, 2010; figures for years not ending in 0 or 5 are interpolated.

FIGURE 6-10: Rate of deaths from terrorism, Western Europe, 1970-2007

FIGURE 6-11: Rate of deaths from terrorism, worldwide, except Afghanistan 2001-and Iraq 2003-

Source: Global Terrorism Database, START (National Consortium for the Study of Terrorism and Responses to Terrorism, 2010, http://www. start. umd. edu/gtd/), accessed on April 6, 2010. Data for 1993 are interpolated. World population figures from U. S. Census Bureau, 2010c; the population estimate for 2007 is extrapolated.

Like the graphs we have seen for interstate wars, civil wars, and genocides, this one has a surprise. The first decade of the new millennium -- the dawn of the Age of Terror -- does not show a rising curve, or a new plateau, but a decrease from peaks in the 1980s and early 1990s. Global terrorism rose in the late 1970s and declined in the 1990s for the same reasons that civil wars and genocides rose and fell during those decades. Nationalist movements sprang up in the wake of decolonization, drew support from superpowers fighting the Cold War by proxy, and died down with the fall of the Soviet empire. The bulge in the late 1970s and early 1980s is mainly the handiwork of terrorists in Latin America (El Salvador, Nicaragua, Peru, and Colombia), who were responsible for 61 percent of the deaths from terrorism between 1977 and 1984. (Many of these targets were military or police forces, which the GTD includes in its database as long as the incident was intended to gain the attention of an audience rather than to inflict direct damage.) Latin America kept up its contribution in the second rise from 1985 to 1992 (about a third of the deaths), joined by the Tamil Tigers in Sri Lanka (15 percent) and groups in India, the Philippines, and Mozambique. Though some of the terrorist activity in India and the Philippines came from Muslim groups, only a sliver of the deaths occurred in Muslim countries: around 2 percent of them in Lebanon, and 1 percent in Pakistan. The decline of terrorism since 1997 was punctuated by peaks for 9/11 and by a recent uptick in Pakistan, mainly as a spillover from the war in Afghanistan along their nebulous border.

Though 9/11 did not inaugurate a new age of terror, a case could be made that it foretold an age of Islamist suicide terror. The 9/11 hijackers could not have carried out their attacks had they not been willing to die in the process, and since then the rate of suicide attacks has soared, from fewer than 5 per year in the 1980s and 16 per year in the 1990s to 180 per year between 2001 and 2005. Most of these attacks were carried out by Islamist groups whose expressed motives were at least partly religious. According to the most recent data from the National Counterterrorism Center, in 2008 Sunni Islamic extremists were responsible for almost two-thirds of the deaths from terrorism that could be attributed to a terrorist group.

The numbers, then, show that we are not living in a new age of terrorism. If anything, aside from the wars in Iraq and Afghanistan, we are enjoying a decline in terrorism from decades in which it was less big a deal in our collective consciousness. Nor, until recently, has terrorism been a particularly Muslim phenomenon.

But isn't it today? Shouldn't we expect the suicide terrorists from Al Qaeda, Hamas, and Hezbollah to be picking up the slack? And what are we hiding by taking the civilian deaths in Iraq and Afghanistan, many of them victims of suicide bombers, out of the tallies? Answering these questions will require a closer look at terrorism, especially suicide terrorism, in the Islamic world.

As a means of killing civilians, suicide terrorism is a tactic of diabolical ingenuity. It combines the ultimate in surgical weapon delivery -- the precision manipulators and locomotors called hands and feet, controlled by the human eyes and brain -- with the ultimate in stealth -- a person who looks just like millions of other people. In technological sophistication, no battle robot comes close. The advantages are not just theoretical. Though suicide terrorism accounts for a minority of terrorist attacks, it is responsible for a majority of the casualties. This bang for the buck can be irresistible to the leaders of a terrorist movement. As one Palestinian official explained, a successful mission requires only "a willing young man… nails, gunpowder, a light switch and a short cable, mercury (readily obtainable from thermometers), acetone… The most expensive item is transportation to an Israeli town." The only real technological hurdle is the willingness of the young man. Ordinarily a human being is unwilling to die, the legacy of half a billion years of natural selection. How have terrorist leaders overcome this obstacle?

People have exposed themselves to the risk of dying in wars for as long as there have been wars, but the key term is risk. Natural selection works on averages, so a willingness to take a small chance of dying as part of an aggressive coalition that offers a large chance of a big fitness payoff -- more land, more women, or more safety -- can be favored over the course of evolution. What cannot be favored is a willingness to die with certainty, which would take any genes that allow such willingness along with the dead body. It's not surprising that suicide missions are uncommon in the history of warfare. Foraging bands prefer the safety of raids and ambushes to the hazards of set-piece battles, and even then warriors are not above claiming to have had dreams and omens that conveniently keep them out of risky encounters planned by their comrades.

Modern armies cultivate incentives for soldiers to increase the risk they take on, such as esteem and decorations for bravery, and disincentives for them to reduce the risk, such as the shaming or punishment of cowards and the summary execution of deserters. Sometimes a special class of soldier called file closers trails behind a unit with orders to kill any soldier who fails to advance. The conflicts of interest between war leaders and foot soldiers leads to the well-known hypocrisy of military rhetoric. Here is how a British general waxed about the carnage of World War I: "Not a man shirked going through the extremely heavy barrage, or facing the machine gun and rifle fire that finally wiped them out… I have never seen, indeed could never have imagined, such a magnificent display of gallantry, discipline, and determination." A sergeant described it differently: "We knew it was pointless, even before we went over -- crossing open ground like that. But you had to go. You were between the devil and the deep blue sea. If you go forward, you'll likely be shot. If you go back, you'll be court-martialed and shot. What can you do?"

Warriors may accept the risk of death in battle for another reason. The evolutionary biologist J. B. S. Haldane, when asked whether he would lay down his life for his brother, replied, "No, but for two brothers or eight cousins." He was invoking the phenomenon that would later be known as kin selection, inclusive fitness, and nepotistic altruism. Natural selection favors any genes that incline an organism toward making a sacrifice that helps a blood relative, as long as the benefit to the relative, discounted by the degree of relatedness, exceeds the cost to the organism. The reason is that the genes would be helping copies of themselves inside the bodies of those relatives and would have a long-term advantage over their narrowly selfish alternatives. Critics who are determined to misunderstand this theory imagine that it requires that organisms consciously calculate their genetic overlap with their kin and anticipate the good it will do their DNA. Of course it requires only that organisms be inclined to pursue goals that help organisms that are statistically likely to be their genetic relatives. In complex organisms such as humans, this inclination is implemented as the emotion of brotherly love.

As with all aspects of our psychology that have been illuminated by evolutionary theory, what matters is not actual genetic relatedness (it's not as if hunter-gatherers, to say nothing of chimpanzees, send off cheek swabs to a genotyping service) but the perception of relatedness, as long as the perception was correlated with the reality over long enough spans of time. Among the contributors to the perception of kinship are the experience of having grown up together, having seen one's mother care for the other person, commensal meals, myths of common ancestry, essentialist intuitions of common flesh and blood, the sharing of rituals and ordeals, physical resemblance (often enhanced by hairdressing, tattoos, scarification, and mutilation), and metaphors such as fraternity, brotherhood, family, fatherland, motherland, and blood. Military leaders use every trick in the book to make their soldiers feel like genetic relatives and take on the biologically predictable risks. Shakespeare made this clear in the most famous motivational speech in the literary history of war, when Henry V addresses his men on St. Crispin's Day:

The small-scale bands in which humans spent much of their evolutionary history were held together by kinship, and people tended to be related to their neighbors. Among the Yanomamö, for example, two individuals picked at random from a village are related almost as closely as first cousins, and people who consider each other relatives are related, on average, even more closely. The genetic overlap tilts the evolutionary payoff toward taking greater risks to life and limb if the risky act might benefit one's fellow warriors. One of the reasons that chimpanzees, unlike other primates, engage in cooperative raiding is that the females, rather than the males, disperse from the troop at sexual maturity, so the males in a troop tend to be related.

But we in it shall be rememberèd --

We few, we happy few, we band of brothers;

Modern militaries too take pains to group soldiers into bands of brothers -- the fire teams, squads, and platoons of half a dozen to several dozen soldiers that serve as a crucible for the primary emotion that moves men to fight in armies, brotherly love. Studies of military psychology have discovered that soldiers fight above all out of loyalty to their platoonmates. The writer William Manchester reminisced about his experience as a Marine in World War II:

For he today that sheds his blood with me

And Crispin Crispian shall ne'er go by,

Shall be my brother.

From this day to the ending of the world,

Those men on the line were my family, my home. They were closer to me than I can say, closer than any friends had been or ever would be. They had never let me down, and I couldn't do it to them… I had to be with them, rather than let them die and me live with the knowledge that I might have saved them. Men, I now knew, do not fight for flag or country, for the Marine Corps or glory or any other abstraction. They fight for one another.

Two decades later, another Marine-turned-author, William Broyles, offered a similar reflection on his experience in Vietnam:

The enduring emotion of war, when everything else has faded, is comradeship. A comrade in war is a man you can trust with anything, because you trust him with your life… Despite its extreme right-wing image, war is the only utopian experience most of us ever have. Individual possessions and advantage count for nothing: the group is everything. What you have is shared with your friends. It isn't a particularly selective process, but a love that needs no reasons, that transcends race and personality and education -- all those things that would make a difference in peace.

Though in extremis a man may lay down his life to save a platoon of virtual brothers, it's rarer for him to calmly make plans to commit suicide at some future date on their behalf. The conduct of war would be very different if he did. To avoid panic and rout (at least in the absence of file closers), battle plans are generally engineered so that an individual soldier does not know that he has been singled out for certain death. At a bomber base during World War II, for example, strategists calculated that pilots would have a higher probability of survival if a few of them who drew the short straws in a lottery would fly off to certain death on one-way sorties rather than all of them taking their chances in the fuel-laden planes needed for round trips. But they opted for the higher risk of an unpredictable death over the lower risk of a death that would be preceded by a lengthy period of doom. How do the engineers of suicide terrorism overcome this obstacle?

Using interviews with failed and prospective suicide terrorists, the anthropologist Scott Atran has refuted many common misconceptions about them. Far from being ignorant, impoverished, nihilistic, or mentally ill, suicide terrorists tend to be educated, middle class, morally engaged, and free of obvious psychopathology. Atran concluded that many of the motives may be found in nepotistic altruism.

Certainly an ideology of an afterlife helps, as in the posthumous Playboy Mansion promised to the 9/11 hijackers. (Japanese kamikaze pilots had to make do with the less vivid image of being absorbed into a great realm of the spirit.) But modern suicide terrorism was perfected by the Tamil Tigers, and though the members grew up in Hinduism with its promise of reincarnation, the group's ideology was secular: the usual goulash of nationalism, romantic militarism, Marxism-Leninism, and anti-imperialism that animated 20th-century third-world liberation movements. And in accounts by would-be suicide terrorists of what prompted them to enlist, anticipation of an afterlife, with or without the virgins, seldom figures prominently. So while expectation of a pleasant afterlife may tip the perceived cost-benefit ratio (making it harder to imagine an atheist suicide bomber), it cannot be the only psychological driver.

The case of the Tamil Tigers is relatively easy. They use the terrorist equivalent of file closers, selecting operatives for suicide missions and threatening to kill their families if they withdraw. Only slightly less subtle are the methods of Hamas and other Palestinian terrorist groups, who hold out a carrot rather than a stick to the terrorist's family in the form of generous monthly stipends, lump-sum payments, and massive prestige in the community. Though in general one should not expect extreme behavior to deliver a payoff in biological fitness, the anthropologists Aaron Blackwell and Lawrence Sugiyama have shown that it may do so in the case of Palestinian suicide terrorism. In the West Bank and Gaza many men have trouble finding wives because their families cannot afford a bride-price, they are restricted to marrying parallel cousins, and many women are taken out of the marriage pool by polygynous marriage or by marriage up to more prosperous Arabs in Israel. Blackwell and Sugiyama note that 99 percent of Palestinian suicide terrorists are male, that 86 percent are unmarried, and that 81 percent have at least six siblings, a larger family size than the Palestinian average. When they plugged these and other numbers into a simple demographic model, they found that when a terrorist blows himself up, the financial payoff can buy enough brides for his brothers to make his sacrifice reproductively worthwhile.

Atran has found that suicide terrorists can also be recruited without these direct incentives. Probably the most effective call to martyrdom is the opportunity to join a happy band of brothers. Terrorist cells often begin as gangs of underemployed single young men who come together in cafés, dorms, soccer clubs, barbershops, or Internet chat rooms and suddenly find meaning in their lives by a commitment to the new platoon. Young men in all societies do foolish things to prove their courage and commitment, especially in groups, where individuals may do something they know is foolish because they think that everyone else in the group thinks it is cool. (We will return to this phenomenon in chapter 8.) Commitment to the group is intensified by religion, not just the literal promise of paradise but the feeling of spiritual awe that comes from submerging oneself in a crusade, a calling, a vision quest, or a jihad. Religion may also turn a commitment to the cause into a sacred value -- a good that may not be traded off against anything else, including life itself. The commitment can be stoked by the thirst for revenge, which in the case of militant Islamism takes the form of vengeance for the harm and humiliation suffered by any Muslim anywhere on the planet at any time in history, or for symbolic affronts such as the presence of infidel soldiers on sacred Muslim soil. Atran summed up his research in testimony to a U. S. Senate subcommittee:

The local imams are of marginal importance in this radicalization, since young men who want to raise hell rarely look to community elders for guidance. And Al Qaeda has become more a global brand inspiring a diffuse social network than a centralized recruiting organization.

When you look at young people like the ones who grew up to blow up trains in Madrid in 2004, carried out the slaughter on the London underground in 2005, hoped to blast airliners out of the sky en route to the United States in 2006 and 2009, and journeyed far to die killing infidels in Iraq, Afghanistan, Pakistan, Yemen or Somalia; when you look at whom they idolize, how they organize, what bonds them and what drives them; then you see that what inspires the most lethal terrorists in the world today is not so much the Koran or religious teachings as a thrilling cause and call to action that promises glory and esteem in the eyes of friends, and through friends, eternal respect and remembrance in the wider world that they will never live to enjoy… Jihad is an egalitarian, equal-opportunity employer:… fraternal, fastbreaking, thrilling, glorious, and cool. Anyone is welcome to try his hand at slicing off the head of Goliath with a paper cutter.

The up-close look at suicide terrorists at first seems pretty depressing, because it suggests we are fighting a multiheaded hydra that cannot be decapitated by killing its leadership or invading its home base. Remember, though, that all terrorist organizations follow an arc toward failure. Are there any signs that Islamist terrorism is beginning to burn out?

The answer is a clear yes. In Israel, sustained attacks on civilians have accomplished what they accomplish everywhere else in the world: erase all sympathy for the group, together with any willingness to compromise with it. After the Second Intifada began, shortly after Yasir Arafat's rejection of the Camp David accords in 2000, the Palestinians' economic and political prospects steadily deteriorated. In the long run, Cronin adds, suicide terrorism is a supremely idiotic tactic because it makes the target nation unwilling to tolerate members of the minority community in their midst, never knowing which among them may be a walking bomb. Though Israel has faced international condemnation for building a security barrier, other countries faced with suicide terrorism, Cronin notes, have taken similar measures. The Palestinian leadership on the West Bank has, more recently, disavowed violence and turned its energies toward competent governance, while Palestinian activist groups have turned to boycotts, civil disobedience, peaceful protests, and other forms of nonviolent resistance. They have even enlisted Rajmohan Gandhi (grandson of Mohandas) and Martin Luther King III for symbolic support. It's too soon to know whether this is a turning point in Palestinian tactics, but a retreat from terrorism would not be historically unprecedented.

The bigger story, though, is the fate of Al Qaeda. Marc Sageman, a former CIA officer who has been keeping tabs on the movement, counted ten serious plots on Western targets in 2004 (many inspired by the invasion of Iraq) but just three in 2008. Not only has Al Qaeda's base in Afghanistan been routed and its leadership decimated (including bin Laden himself in 2011), but in the world of Muslim opinion its favorables have long been sinking, and its negatives have been rising. In the past six years Muslims have become repulsed by what they increasingly see as nihilistic savagery, consistent with Cronin's remark that decency, not just violence, has an international language. The movement's strategic goals -- a pan-Islamic caliphate, the replacement of repressive and theocratic regimes by even more repressive and theocratic regimes, the genocidal killing of infidels -- begin to lose their appeal once people start thinking about what they really mean. And Al Qaeda has succumbed to the fatal temptation of all terrorist groups: to stay in the limelight by mounting ever bloodier attacks on ever more sympathetic victims, which in Al Qaeda's case includes tens of thousands of fellow Muslims. Attacks in the mid-2000s on a Bali nightclub, a Jordanian wedding party, an Egyptian resort, the London underground, and cafés in Istanbul and Casablanca massacred Muslims and non-Muslims alike for no discernible purpose. The franchise of the movement known as Al Qaeda in Iraq (AQI) proved to be even more depraved, bombing mosques, marketplaces, hospitals, volleyball games, and funerals, and brutalizing resisters with amputations and beheadings.

The jihad against the jihadis is being fought at many levels. Islamic states such as Saudi Arabia and Indonesia that once indulged Islamist extremists have decided that enough is enough and have begun to crack down. The movement's own gurus have also turned on it. In 2007 one of bin Laden's mentors, the Saudi cleric Salman al-Odah, wrote an open letter accusing him of "fostering a culture of suicide bombings that has caused bloodshed and suffering, and brought ruin to entire Muslim communities and families." He was not afraid to get personal: "My brother Osama, how much blood has been spilt? How many innocent people, children, elderly, and women have been killed… in the name of Al Qaeda? Will you be happy to meet God Almighty carrying the burden of these hundreds of thousands or millions on your back?" His indictment struck a chord: two-thirds of the postings on Web sites of Islamist organizations and television networks were favorable, and he has spoken to enthusiastic crowds of young British Muslims. The grand mufti of Saudi Arabia, Abdulaziz al Ash-Sheikh, made it official, issuing a fatwa in 2007 forbidding Saudis to join foreign jihads and condemning bin Laden and his cronies for "transforming our youth into walking bombs to accomplish their own political and military aims." That same year another sage of Al Qaeda, the Egyptian scholar Sayyid Imam Al Sharif (also known as Dr. Fadl), published a book called Rationalization of Jihad because, he explained, "Jihad… was blemished with grave Sharia violations during recent years… Now there are those who kill hundreds, including women and children, Muslims and non-Muslims in the name of Jihad!"

The Arab street agrees. In a 2008 online Q& A on a jihadist Web site with Ayman al-Zawahiri, Al Qaeda's day-to-day leader, one participant asked, "Excuse me, Mr. Zawahiri, but who is it who is killing, with Your Excellency's blessing, the innocents in Baghdad, Morocco, and Algeria?" Public opinion polls throughout the Islamic world have tapped the outrage. Between 2005 and 2010, the number of respondents in Jordan, Pakistan, Indonesia, Saudi Arabia, and Bangladesh who endorse suicide bombing and other violence against civilians has sunk like a stone, often to around 10 percent. Lest even this figure seem barbarically high, the political scientist Fawaz Gerges (who compiled the data) reminds us that no fewer than 24 percent of Americans tell pollsters that "bombing and other attacks intentionally aimed at civilians are often or sometimes justified."

More important is public opinion in the war zones in which the terrorists rely on the support of the population. In the North-West Frontier Province in Pakistan, support for Al Qaeda plummeted from 70 percent to 4 percent in just five months in late 2007, partly in reaction to the assassination of former prime minister Benazir Bhutto by a suicide bomber. In elections that year Islamists won 2 percent of the national vote -- a fivefold decrease since 2002. In a 2007 ABC/BBC poll in Afghanistan, support for jihadist militants nosedived to 1 percent. In Iraq in 2006 a large majority of Sunnis and an overwhelming majority of Kurds and Shias rejected AQI, and by December 2007 the opposition to their attacks on civilians had reached a perfect 100 percent.

Public opinion is one thing, but does it translate into a reduction of violence? Terrorists depend on popular support, so it's highly likely that it does. The year 2007, the turning point in attitudes toward terrorism in the Islamic world, was also a turning point in suicide attacks in Iraq. The Iraq Body Count has documented that vehicle bombs and suicide attacks declined from 21 a day in 2007 to fewer than 8 a day in 2010-- still too many, but a sign of progress. Changes in Muslim attitudes do not deserve all the credit; the surge of American soldiers in the first half of 2007 and other military adjustments helped as well. But some of the military developments themselves depended on a shift in attitudes. Muqtada al-Sadr's Mahdi Army, a Shia militia, declared a cease-fire in 2007, and in what has been called the Sunni Awakening tens of thousands of young men have defected from an insurgency against the American-supported government and are participating in the suppression of Al Qaeda in Iraq.

Terrorism is a tactic, not an ideology or a regime, so we will never win the "War on Terror," any more than we will achieve George W. Bush's larger goal (announced in the same post-9/11 speech) to "rid the world of evil." In an age of global media, there will always be an ideologue nursing a grievance somewhere who is tempted by the spectacular return on investment of terrorism -- a huge windfall in fear from a trifling outlay in violence -- and there will always be bands of brothers willing to risk everything for the comradeship and glory it promises. When terrorism becomes a tactic in a large insurgency, it can do tremendous damage to people and to civil life, and the hypothetical threat of nuclear terrorism (to which I will turn in the final section) gives new meaning to the word terror. But in every other circumstance history teaches, and recent events confirm, that terrorist movements carry the seeds of their own destruction.