Holding down the fort: in Chilas, British India, 1898. (Getty Images / Hulton Archive).

Pundits and the press too often treat terrorism and guerrilla tactics as something new, a departure from old-fashioned ways of war. But nothing could be further from the truth. Throughout most of our species' long and bloody slog, warfare has primarily been carried out by bands of loosely organized, ill-disciplined, and lightly armed volunteers who disdained open battle in favor of stealthy raids and ambushes: the strategies of both tribal warriors and modern guerrillas and terrorists. In fact, conventional warfare is the relatively recent invention. It was first made possible after 10,000 BC by the development of agricultural societies, which produced enough surplus wealth and population to allow for the creation of specially designed fortifications and weapons (and the professionals to operate them). The first genuine armies -- commanded by a strict hierarchy, composed of trained soldiers, disciplined with threats of punishment -- arose after 3100 BC in Egypt and Mesopotamia. But the process of state formation and, with it, army formation took considerably longer in most of the world. In some places, states emerged only in the past century, and their ability to carry out such basic functions as maintaining an army remains tenuous at best. Considering how long humans have been roaming the earth, the era of what we now think of as conventional conflict represents the mere blink of an eye.

Nonetheless, since at least the days of the Greeks and the Romans, observers have belittled irregular warfare. Western soldiers and scholars have tended to view it as unmanly, even barbaric. It's not hard to see why: guerillas, in the words of the British historian John Keegan, are "cruel to the weak and cowardly in the face of the brave" -- precisely the opposite of what professional soldiers are taught to be. Many scholars have even claimed that guerrilla raids are not true warfare.

This view comes to seem a bit ironic when one considers the fact that throughout history, irregular warfare has been consistently deadlier than its conventional cousin -- not in total numbers killed, since tribal societies are tiny compared with urban civilizations, but in the percentage killed. The average tribal society loses 0.5 percent of its population in combat every year. In the United States, that would translate into 1.5 million deaths, or 500 September 11 attacks a year. Archaeological evidence confirms that such losses are not a modern anomaly.

The origins of guerilla warfare are lost in the swamps of prehistory, but the kinds of foes that guerrillas have faced have changed over the centuries. Before about 3000 BC, tribal guerrillas fought exclusively against other tribal guerrillas. Although that type of fighting continued after 3000 BC, it was supplemented and sometimes supplanted by warfare pitting tribes and rebels against newly formed states. These conflicts were, in a sense, the world's first insurgencies and counterinsurgencies. Every great empire of antiquity, starting with the first on record, the Akkadian empire, in ancient Mesopotamia, was deviled by nomadic guerrillas, although the term "guerrilla" would not be coined for millennia to come. ("Guerrilla," literally meaning "small war," dates to the Spanish resistance against Napoleon, from 1808 to 1814.)

In modern times, the same old guerrilla tactics have been married to ideological agendas, something that was utterly lacking among the apolitical (and illiterate) tribal warriors of old. Of course, the precise nature of the ideological agendas being fought for has changed over the years, from liberalism and nationalism (the cri de coeur of guerrilla fighters from the late eighteenth century to the late nineteenth century), to socialism and nationalism (which inspired guerrillas between the late nineteenth century and the late twentieth century), to jihadist extremism today. All the while, guerrilla and terrorist warfare have remained as ubiquitous and deadly as ever.

THE GUERRILLA PARADOX

The success of various raiders in attacking and conquering states from ancient Rome to medieval China gave rise to what one historian has called "the nomad paradox." "In the history of warfare, it has generally been the case that military superiority lies with the wealthiest states and those with the most developed administrations," the historian Hugh Kennedy wrote in Mongols, Huns, and Vikings. Yet going back to the days of Mesopotamia, nomads often managed to bring down far richer and more advanced empires. Kennedy explains this seeming contradiction by citing all the military advantages nomads enjoyed: they were more mobile, every adult male was a warrior, and their leaders were selected primarily for their war-making prowess. By contrast, he notes, settled societies appointed commanders based on political considerations and drafted as soldiers farmers with scant martial skills.

Nomads' military advantages seem to have persisted among guerrillas in the modern world; even in the last two centuries, during which states became far more powerful than in the ancient or the medieval period, guerrillas often managed to humble them. Think of the tribes of Afghanistan, which frustrated the United Kingdom, the Soviet Union, and the United States. Kennedy's "nomad paradox" is really a guerrilla paradox, and it asks how and why the weak seem to so frequently defeat the strong. The answer lies largely in the use of hit-and-run tactics, taking advantage of mobility and surprise to make it difficult for the stronger state to bring its full weight to bear.

Guerrillas often present a further paradox: even the most successful raiders have been prone to switch to conventional tactics once they achieve great military success. The Mongols eventually turned into a semiregular army under Genghis Khan, and the Arabs underwent a similar transformation. They fought in traditional Bedouin style while spreading Islam across the Middle East in the century after Muhammad's death, in 632. But their conquests led to the creation of the Umayyad and Abbassid caliphates, two of the greatest states of the medieval world, which were defended by conventional forces. The Turkish empire, too, arose out of the raiding culture of the steppes but built a formidable conventional army, complete with highly disciplined slave-soldiers, the janissaries. The new Ottoman army conquered Constantinople in a famous siege in 1453 and, within less than a century, advanced to the gates of Vienna.

Why did nomads so adept at guerrilla tactics resort to conventional warfare? For one thing, their targets became bigger, requiring a shift in tactics. Mounted archers could not have taken Constantinople; that feat required the mechanics of a proper military, including a battery of 69 cannons, two of which were 27 feet long and fired stone balls that weighed more than half a ton. Nor were fast-moving tribal fighters of much use in defending, administering, and policing newly conquered states. Those tasks, too, required a professional standing army. A further factor dictated the transformation of nomads into regulars: the style of fighting practiced by mounted archers was so difficult and demanding that it required constant practice from childhood on for an archer to maintain proficiency. Once nomads began living among more sedentary people, they "easily lost their superior individual talents and unit cohesion," write the historians Mesut Uyar and Edward Erickson in A Military History of the Ottomans. This was a tradeoff that most of them were happy to make. A settled life was much easier -- and safer.

The nomads' achievements, although great, were mostly fleeting: with the exception of the Arabs, the Turks, the Moguls, and the Manchu, who blended into settled societies, nomads could not build lasting institutions. Nomadic empires generally crumbled after a generation or two. Former nomads who settled down found themselves, somewhat ironically, beset by fresh waves of nomads and other guerrillas. Such was the fate of the Manchu, who, as the rulers of China, fought off the Dzungar (or western Mongols) in the eighteenth century and tried to fight off the Taiping rebels in the deadliest war of the nineteenth century. The Taipings, in turn, tried to develop more powerful armies of their own, blurring the distinction between regular and irregular conflict. Since then, many civil wars, including the one the United States fought between 1861 and 1865, have featured both kinds of combat.

IRREGULARS IN THE AGE OF REASON

The dividing line between regular and irregular warfare grew more distinct with the spread of standing national armies after the Thirty Years' War. That process, which went hand in hand with the growth of nation-states, came to a head in the second half of the seventeenth century. The period saw the proliferation of barracks to house soldiers, drillmasters to train them, professional officers to lead them, logistical services to supply them, factories to clothe and equip them, and hospitals and retirement homes to take care of them.

By the eighteenth century, Western warfare had reached stylized heights seldom seen before or since, with monarchical armies fighting in roughly similar styles and abiding by roughly similar rules of conduct. No change was more important than the adoption of standardized uniforms, which meant that the difference between soldiers and civilians could be glimpsed in an instant. Fighters who insisted on making war without uniforms therefore became more easily distinguished. They were subject to prosecution as bandits rather than treated as soldiers entitled to the protections of the emerging laws of war.

But irregulars soon returned to prominence, during the War of the Austrian Succession (1740-48), a conflict pitting Austria, Great Britain, Hanover, Hesse, and the Netherlands against Bavaria, France, Prussia, Saxony, and Spain. Austria lost the war's early battles, allowing foreign troops to occupy a substantial portion of its territory. But Austria managed a comeback thanks to so-called wild men it mustered from the fringes of its empire: hussars from Hungary, pandours from Croatia, and other Christians from the Balkans who had been fighting the Turks for centuries.

Frederick the Great and other generals at first denounced the raiders as "savages." But as soon as they saw the irregulars' effectiveness, they copied the Austrian example. By the 1770s, light troops (skirmishers lacking heavy weapons and armor who did not stand in the main battle line) made up 20 percent of most European armies. In North America, the British army came increasingly to rely on a variety of light infantry. Precursors to today's special forces -- troops trained in guerrilla tactics who are nonetheless still more disciplined than stateless fighters -- these "rangers" were raised for "wood service," or irregular combat, against French colonial troops and their native allies.

One of the cherished myths of American history is that plucky Yankees won independence from Great Britain by picking off befuddled redcoats too dense to deviate from ritualistic parade-ground warfare. That is an exaggeration. By the time the Revolution broke out, in 1775, the British were well versed in irregular warfare and were countering it in Europe, the Caribbean, and North America. Redcoats certainly knew enough to break ranks and seek cover in battle when possible, rather than, in the words of one historian, "remaining inert and vulnerable to enemy fire." The British army had a different problem: much like the modern U.S. Army pre-Iraq, it had forgotten most of the lessons of irregular war learned a generation before. And the American rebels used a more sophisticated form of irregular warfare than the French backwoodsmen and Native American warriors whom the redcoats had gotten used to fighting. The spread of literacy and printed books allowed the American insurgents to appeal for popular support, thereby elevating the role of propaganda and psychological warfare. It is appropriate that the term "public opinion" first appeared in print in 1776, for the American rebels won independence in large part by appealing to the British electorate with documents such as Thomas Paine's pamphlet Common Sense and the Declaration of Independence. In fact, the outcome of the Revolution was really decided in 1782, when the British House of Commons voted by a narrow margin to discontinue offensive operations. The British could have kept fighting after that date; they could have raised fresh armies even after the defeat at Yorktown in 1781. But not after they had lost the support of parliament.

Most of the revolutionaries who followed were more extreme in their methods and beliefs than the American rebels, but, whether left or right, many of them copied the Americans' skillful manipulation of public opinion. The Greeks in the 1820s, the Cubans in the 1890s, and the Algerians in the 1950s all enjoyed notable success mobilizing foreign opinion to help win their independence. In Greece and Cuba, the anti-imperialists won by highlighting the colonies' suffering to spur what would today be called humanitarian interventions by Western powers.

Liberal insurgents scored their most impressive victories in the New World. With a few exceptions, by 1825, the European colonial powers had been defeated in the Americas. European revolts at home, such as that of the Chartists in the United Kingdom and that of the Decembrists in Russia, were less successful. Still, by the turn of the twentieth century, most of Europe and North America was moving in a more liberal direction -- even those absolute monarchies, such as Austria, Germany, and Russia, that remained as such were making greater efforts to appease and direct popular sentiment.

WARS THAT WEREN'T

At the same time, Western states were extending their rule across much of the rest of the world in a decidedly illiberal fashion. The process of colonization and resistance would do much to shape the modern world and would give rise to the most influential counterinsurgency doctrine of all time: the "oil spot" theory, coined by the French marshal Hubert Lyautey, who in fin-de-siècle Indochina, Madagascar, and Morocco anticipated the "population-centric" doctrine that U.S. forces implemented in Afghanistan and Iraq in the twenty-first century. It involved slowly extending army posts and settlements, like a spreading oil spot, until indigenous resistance was crushed, while also trying to address locals' political and economic concerns.

The people of Asia and Africa resisted the colonists' advance as best they could. Sometimes, they were able to force serious setbacks; a famous example was the 1842 British retreat from Kabul. But these were only temporary reversals in the inexorable westernization of the world. By 1914, Europeans and their offspring controlled 84 percent of the world's landmass, up from 35 percent in 1800.

That non-Europeans did not have more success in preserving their independence was due in large measure to Europe's growing advantages in military technology and technique. But it also owed something to the fact that most non-Europeans did not adopt strategies that made the best use of their limited resources. Instead of attempting to engage in guerrilla warfare -- which, even if unsuccessful, might have staved off ultimate defeat for years, if not decades, and inflicted considerable costs on the invaders -- most non-Europeans fought precisely as the Europeans wanted them to, that is to say, in conventional fashion.

Westerners thought that most of the areas they conquered were "primitive" and "backward," but in a sense, they were too advanced for their own good. By the time Europeans marched into Asia and Africa, much of those continents had fallen under the sway of native regimes with standing armies, such as the Zulu empire in southern Africa and the Maratha empire in India. Their rulers naturally looked to those standing armies for protection, typically eschewing the sort of tribal tactics (a primitive form of guerrilla warfare) practiced by their ancestors. In most cases, the decisions quickly backfired. When native rulers did try to correct course, their impulse was usually to make their armies even more conventional by hiring European advisers and buying European arms. The reproductions were seldom as good as the originals, however, and their inferiority was brutally exposed in battle.

Why did so few indigenous regimes resort to guerrilla tactics? In part, because non-Westerners had little idea of the combat power of Western armies until it was too late. Too many indigenous empire builders in the developing world imagined that the tactics they had used to conquer local tribes would work against the white invaders as well. Even if those rulers had wanted to ignite insurgencies, moreover, the ideological fuel was generally lacking, save in Algeria, Chechnya and Dagestan, and a few other areas where Muslim rebels waged prolonged wars of resistance against European colonists. Often, the subjects of these regimes resented the indigenous rulers as much as, if not more than, the European invaders. Nationalism, a relatively recent invention, had not yet spread to those lands.

European soldiers in "small wars" were helped by the fact that most of the fighting occurred on the periphery of their empires in Asia and Africa against enemies that were considered "uncivilized" and therefore, under the European code of conduct, could be fought with unrestrained ferocity. As late as the 1930s, the British officer and novelist John Masters wrote that on the northwest frontier of India (today's Pakistan), Pashtun warriors "would usually castrate and behead" captives, whereas the British "took few prisoners at any time, and very few indeed if there was no Political Agent about" -- they simply killed those they captured. The very success of the imperial armies meant that future battles would take place within imperial boundaries, however, and that they would be, as the historian Thomas Mockaitis wrote in British Counterinsurgency, "considered civil unrest rather than war." Accordingly, imperial troops in the future would find their actions circumscribed by law and public opinion in ways that they had not been in the nineteenth century.

The civil unrest of the twentieth century was harder to deal with for other reasons as well. By setting up schools and newspapers that promulgated Western ideas such as nationalism and Marxism, Western administrators eventually spurred widespread resistance to their own rule. And by manufacturing and distributing countless weapons, from TNT to the AK-47, all over the world, the Europeans ensured that their twentieth-century opponents were far better armed than their predecessors had been.

THE SUN SETS ON THE BRITISH EMPIRE

To understand why decolonization swept the world in the late 1940s and why anti-Western guerrillas and terrorists fared so well during that period, it is vital to underscore how weak the two biggest colonial powers were by then. Even if France and the United Kingdom had been determined to hold on to all their overseas possessions after 1945, they would have been hard-pressed to do so. Both were essentially bankrupt and could not comfortably fight a prolonged counterinsurgency -- especially not in the face of hostility from the rising superpowers. The Soviets, and later the Chinese, were always ready to provide arms, training, and financing to national liberation movements of a Marxist bent.

Most of the decolonization process was relatively peaceful. Where the British did face determined opposition, as in India and Palestine, it did not take much to persuade them to leave. London generally only fought to hold on to a few bases, such as Cyprus and Aden, that it deemed to be of strategic significance or, as in Malaya and Kenya, to prevent a takeover by Communists or other extremists. When the British did choose to fight, they did so skillfully and successfully; their counterinsurgency record is better than that of the French during the same period, and some of their campaigns, notably that in Malaya, are still studied by military strategists.

The incidence of guerrilla warfare and terrorism did not decline with the demise of the European empires. On the contrary, the years between 1959 and 1979 -- from Fidel Castro's takeover in Cuba to the Sandinistas' takeover in Nicaragua -- were, if anything, the golden age of leftist insurgency. There remained a few colonial wars and a larger number of essentially ethnic wars (in Congo, East Timor, and Nigeria's Biafra region) fought to determine the nature of postcolonial states, but the primary driver was socialist ideology. Radicals who styled themselves as the next Mao, Ho, Fidel, or Che took up Kalashnikovs to wage rural guerrilla warfare and urban terrorism. Never before or since has the glamour and prestige of irregular warriors been higher, as seen in the ubiquity of the artist Alberto Korda's famous photograph of Che Guevara, which still adorns T-shirts and posters. The success of revolutionaries abroad resounded among the Western radicals of the 1960s, who were discontented with their own societies and imagined that they, too, could overthrow the establishment. Tom Wolfe captured the moment in his famous 1970 essay "Radical Chic," which described in excruciating detail a party thrown by the composer Leonard Bernstein in his swank New York apartment for a group of Black Panthers, one of myriad terrorist groups of a period whose fame far exceeded its ability to achieve its goals.

Some governments had considerable success in suppressing insurgent movements. The 1960s saw the publication of influential manuals such as Counterinsurgency Warfare: Theory and Practice, by the French officer (and Algeria veteran) David Galula, and Defeating Communist Insurgency, by the British official Sir Robert Thompson, a suave veteran of Malaya and Vietnam. Galula, Thompson, and other experts reached a remarkable degree of agreement that insurgencies could not be fought like conventional wars. The fundamental principle that set counterinsurgency apart was the use of "the minimum of fire." Meanwhile, a "soldier must be prepared to become a propagandist, a social worker, a civil engineer, a schoolteacher, a nurse, a boy scout," Galula wrote.

It was one thing to generate such hard-won lessons. Altogether more difficult was to get them accepted by military officers whose ideal remained the armored blitzkrieg and who had nothing but contempt for lightly armed ragtag fighters. Western militaries marched into the next few decades still focused on fighting a mirror-image foe. When the United States had to confront a guerrilla threat in Vietnam, William Westmoreland, the commander of U.S. operations there, formulated an overwhelmingly conventional response that expended lots of firepower and destroyed lives on both sides but did not produce victory.

LEFT OUT

Like everyone else, guerrillas and terrorists are subject to popular moods and intellectual fads. By the 1980s, as memories of colonialism faded, as the excesses of postcolonial rulers became more apparent, and as the desirability of capitalism was revived under U.S. President Ronald Reagan and British Prime Minister Margaret Thatcher, leftist movements went into eclipse and the guerrilla mystique faded. Few but the most purblind ideologues could imagine that the future was being born in impoverished and oppressed Cambodia or Cuba. The end of the old regime in Moscow and the gradual opening in Beijing had a more direct impact on insurgent groups, too, by cutting off valuable sources of subsidies, arms, and training. The Marxist terrorist groups of the 1970s, such as the Italian Red Brigades and the German Baader-Meinhof Gang, were never able to generate significant support bases of their own and languished along with their foreign backers. Nationalist movements, such as the Palestine Liberation Organization (PLO) and the Irish Republican Army, fared better, although they were also hobbled by a decline in outside support.

Although leftist insurgencies were on the wane, however, guerrilla warfare and terrorism hardly disappeared. They simply assumed different forms as new militants motivated by the oldest grievances of all -- race and religion -- shot their way into the headlines. The transition from politically motivated to religiously motivated insurgencies was the product of decades, even centuries, of development. It could be traced back to, among other things, the writings of the Egyptian agitator Sayyid Qutb in the 1950s and 1960s; the activities of Hasan al-Banna, who founded Egypt's Muslim Brotherhood in 1928; and the proselytizing of Muhammad ibn Abd al-Wahhab, who in the eighteenth century created the puritanical movement that would one day become the official theology of Saudi Arabia. But the epochal consequences of these religious leaders' ideas did not seize the world's attention until the fateful fall of 1979, when protesters occupied the U.S. embassy in Tehran. The embassy takeover had been organized by radical university students, including the future Iranian president Mahmoud Ahmadinejad, who wanted to strike a blow at "the Great Satan" and domestic secularists. It was followed by the militant takeover of the Grand Mosque in Mecca, the holiest shrine in Islam, and the burning of the U.S. embassy in Islamabad. And then, on December 24, 1979, the Soviets marched into Afghanistan, thus inspiring the mobilization of a formidable force of holy guerrillas: the mujahideen.

The threat from Islamist extremists, which had been building sub rosa for decades, burst into bloody view on September 11, 2001, when al Qaeda staged the deadliest terrorist attack of all time. Previous terrorist organizations, from the PLO to various anarchist groups, had limited the scale of their violence. As the terrorism analyst Brian Jenkins wrote in the 1970s, "Terrorism is theater. . . . Terrorists want a lot of people watching, not a lot of people dead." Al Qaeda and its ilk rewrote that playbook in the United States and Iraq.

To defend itself, the United States and its allies erected a variety of defenses. Mostly, this involved improved security, police work, and intelligence gathering. Militaries played an important role, too, although seldom as central as in Afghanistan and Iraq -- countries whose governments were toppled by American invasions. In states with functioning or semi-functioning governments, such as the Philippines and Saudi Arabia, the U.S. role was limited to providing training, weapons, intelligence, and other assistance to help those governments fight the extremists.

Beyond the West's efforts against al Qaeda, popular protests in the Middle East have dealt terrorist organizations another blow. The Arab Spring has proved to be far more potent an instrument of change than suicide bombings. Even before the death of Osama bin Laden, in 2011, the Pew Global Attitudes Project had recorded a sharp drop in those expressing "confidence" in him: between 2003 and 2010, the figure fell from 46 percent to 18 percent in Pakistan, from 59 percent to 25 percent in Indonesia, and from 56 percent to 14 percent in Jordan.

Even a small minority is enough to sustain a terrorist group, however, and al Qaeda has shown an impressive capacity to regenerate itself. Its affiliates still operate from the Middle East to Southeast Asia. Meanwhile, other Islamist groups continue to show considerable strength in Afghanistan and Pakistan, Hamas controls the Gaza Strip, Hezbollah holds sway in Lebanon, al Shabab bids for power in Somalia, Boko Haram advances in Nigeria, and two newer groups, Ansar Dine and the Movement for Unity and Jihad in West Africa, have taken control of northern Mali. Notwithstanding bin Laden's death and other setbacks to al Qaeda central, the war against Islamist terrorism is far from won. The 9/11 attacks serve as a reminder that seeming security against an invisible army can turn to vulnerability with shocking suddenness and that, unlike the more geographically restricted insurgents of the past, international terrorist groups, such as al Qaeda, can strike almost anywhere.

SMALL WARS, BIG LESSONS

The long history of low-intensity conflict reveals not only how ubiquitous guerrilla warfare has been but also how often its importance has been ignored, thus setting the stage for future humiliations at the hands of determined irregulars. The U.S. Army has a particularly dismaying record of failing to adapt to "small wars," despite its considerable experience fighting Native Americans, Philippine insurrectos, the Vietcong, al Qaeda, the Taliban, and numerous other irregulars. To avoid similar calamities in the future, today's soldiers and policymakers need to accurately appraise the strengths and weaknesses of insurgents.

It is important neither to underestimate nor to overestimate the potency of guerrilla warfare. Before 1945, since irregulars refused to engage in face-to-face battle, they were routinely underestimated. After 1945, however, popular sentiment swung too far in the other direction, enshrining guerrillas as superhuman figures. The truth lies somewhere in between: insurgents have honed their craft since 1945, but they still lose most of the time. Their growing success is due to the spread of communications technology and the increasing influence of public opinion. Both factors have sapped the will of states to engage in protracted counterinsurgencies, especially outside their own territories, and have heightened the ability of insurgents to survive even after suffering military setbacks.

In the fight against insurgents, conventional tactics don't work. To defeat them, soldiers must focus not on chasing guerrillas but on securing the local population. Still, effective population-centric counterinsurgency is not as touchy-feely as commonly supposed. It involves much more than winning "hearts and minds" -- a phrase invented by Sir Henry Clinton, a British general during the American Revolution, and popularized by Sir Gerald Templer, a general during the Malayan Emergency, in the late 1940s and 1950s. The only way to gain control is to garrison troops 24 hours a day, seven days a week, among the civilians; periodic "sweep" or "cordon and search" operations fail, even when conducted by counterinsurgents as cruel as the Nazis, because civilians know that the rebels will return the moment the soldiers leave.

Although control can be imposed at gunpoint, it can be maintained only if the security forces have some degree of popular legitimacy. In years past, it was not hard for foreign empires to gain the necessary legitimacy. But now, with nationalist sentiment having spread to every corner of the world, foreign counterinsurgents, such as the United States, face a tricky task, trying to buttress homegrown regimes that can win the support of their people and yet will still cooperate with the United States.

What makes counterinsurgency all the more difficult is that there are few quick victories in this type of conflict. Since 1775, the average insurgency has lasted seven years (and since 1945, it has lasted almost ten years). Attempts by either insurgents or counterinsurgents to short-circuit the process usually backfire. The United States tried to do just that in the early years of both the Vietnam War and the Iraq war by using its conventional might to hunt down guerrillas in a push for what John Paul Vann, a famous U.S. military adviser in Vietnam, rightly decried as "fast, superficial results." It was only when the United States gave up hopes of a quick victory, ironically, that it started to get results, by implementing the tried-and-true tenets of population-centric counterinsurgency. In Vietnam, it was already too late, but in Iraq, the patient provision of security came just in time to avert an all-out civil war.

The experiences of the United States in Iraq in 2007-8, Israel in the West Bank during the second intifada, the British in Northern Ireland, and Colombia in its ongoing fight against the FARC (Revolutionary Armed Forces of Colombia) show that it is possible for democratic governments to fight insurgents effectively if they pay attention to what the U.S. military calls "information operations" (also known as "propaganda" and "public relations") and implement some version of a population-centric strategy. But these struggles also show that one should never enter into counterinsurgency lightly. Such wars are best avoided if possible. Even so, it is doubtful that the United States will be able to avoid them in the future any more than it has in the past. Given the United States' demonstrations of its mastery of conventional combat in Iraq in 1991 and 2003, few adversaries in the future will be foolish enough to put tank armies in the desert against an American force. Future foes are unlikely, in other words, to repeat the mistake of nineteenth-century Asians and Africans who fought European invaders in the preferred Western style. Guerrilla tactics, on the other hand, are proven effective, even against superpowers.

In the future, irregulars might become deadlier still if they can get their hands on a weapon of mass destruction, especially a nuclear bomb. If that were to happen, a small terrorist cell the size of a platoon might gain more killing capacity than the entire army of a nonnuclear state. That is a sobering thought. It suggests that in the future, low-intensity conflict could pose even greater problems for the world's leading powers than it has in the past -- and those problems were already vexing enough.