The opening shot in the war launched by Al Qaeda was fired not on September 11 but two days before. On September 9, two Tunisian Arabs, posing as journalists and carrying forged Belgian passports, insinuated themselves into the presence of Ahmed Shah Massoud, the leader of Afghanistan's anti-Taliban Northern Alliance. As they began their questioning, they detonated a bomb hidden in a television camera. Massoud died a few days later.

With ample reason (though wrongly, as things turned out), Al Qaeda and its Taliban allies believed that taking out the charismatic Massoud might cripple the Northern Alliance. The bold, clever assassination seemed a case study in the kind of asymmetric warfare—that is, warfare aiming at key enemy vulnerabilities rather than at the enemy's main force—that had flummoxed American forces in Vietnam and might soon flummox them again in Afghanistan.

Here is something that Al Qaeda didn't know: For a century or more, the United States made a specialty of fighting small wars against elusive foes that used asymmetric tactics. And no one ever did it better.

In 1915, the United States landed about 2,000 Marines in Haiti. Chaos there threatened U.S. interests and raised the possibility of opportunistic German meddling. The American forces quickly installed a government and then set out to pacify the countryside held by warlords and guerrillas called cacos. Within a few months, the Marines had established control over a country of 2 million people. The cost: three American dead and 18 wounded, writes journalist Max Boot. "It was a virtuoso display of counterinsurgency warfare."

In 1919, a second caco revolt erupted, led by a formidable commander formidably named Charlemagne Massena Peralte. "Get Charlemagne," the American leadership ordered. Herman Hanneken, a 26-year-old Marine sergeant from Missouri, got him, not by force but by guile and daring. Hanneken and 20 of his men darkened their skin with lampblack and donned caco rags. Posing as insurgents, they set out after nightfall to report a glorious "victory" in person to Peralte. They managed, just barely, to bluff their way past five rebel checkpoints. "Finally they reached the edge of Charlemagne Peralte's camp," writes Boot. "Just 15 feet away they saw the guerrilla leader illuminated by the reflected light of a campfire. Peralte sensed trouble and was on the verge of melting into the night when Hanneken drew his .45-caliber automatic pistol and put a bullet through his heart." The rest of the party then routed the encampment with a Browning automatic rifle, suffering no casualties. Peralta's death broke the back of the revolution. Eat your heart out, Al Qaeda.

All very inspiring, but surely a Haitian-style "small war," won by wits and adaptability rather than by brute force, is the exception in America's military annals? Surely all-out war, with mighty divisions supplied by saurian logistical tails, is the "American way of war"? Not really. In U.S. military history, the full-scale mobilizations are the exceptions and the smaller actions are the rule; and, despite the lack of overwhelming force, or perhaps because of it, these smaller operations have generally been overwhelmingly successful.

Such is the lesson of Boot's recently published book, The Savage Wars of Peace: Small Wars and the Rise of American Power. It is, for me, the book of the season. Full disclosure: I have known and occasionally worked for Boot (he is an editor at The Wall Street Journal) over the years, and I'm acknowledged in his book for having commented on drafts of several chapters. Actually, I doubt my comments helped, because I made them before 9/11 and its aftermath brought Boot's message—for which the adjective "timely" might have been invented—into eye-opening focus.

Commentators were amazed last fall when, after weeks of air strikes in Afghanistan had produced no visible results, the Taliban suddenly collapsed. Hanneken, Frederick Funston, Chesty Puller, and Smedley Butler would not have been so surprised. They were among the American professional soldiers who, in the late 19th and early 20th centuries, fought small wars all over the world, often against fanatical and shadowy opponents. They triumphed not by deploying raw firepower but by seizing the initiative, inventing tactics on the fly, and out-sneaking and out-maneuvering their stealthy and agile enemies. (In Nicaragua in 1912, the legendary Butler bluffed his small Marine contingent past rebel checkpoints by "waving two little bags of sand in the air yelling 'dynamite.' ")

Afghanistan was, of course, a victory for air power, but it was equally a victory for small-war-style adaptability. By many accounts, what turned the tide was not bombing as such but the landing of small groups of American spotters, who learned to ride around on horseback, laptop computers in hand, so they could send target coordinates to strategic bombers high above. At a talk in Washington recently, a senior Air Force officer remarked that no one had ever thought to use strategic bombers for close-air support, much less from horseback. The grunts on the ground invented this tactic, and it worked.

Between the Civil War and World War II, the United States fought small wars in the American West, China, Russia, Latin America, the Caribbean, and elsewhere. In the process, U.S. forces, especially the Marines, built up a nonpareil expertise in projecting force economically and effectively—often in many places at once, and always with astonishingly few casualties. In the 1930s, the Marines published a "Small Wars Manual." It declared that limited operations with fuzzy objectives—not to annihilate a hostile army but "to establish and maintain law and order by supporting or replacing the civil government in countries or areas in which the interests of the United States have been placed in jeopardy"—now represented "the normal and frequent operations of the Marine Corps."

Then two cataclysms swept away that accumulated knowledge. The first was World War II, which established massive deployments as the template for American warfare. The second was the Cold War, in which deterrence by overwhelming force was the name of the superpower game. In Vietnam, the Pentagon fought a classic small-war insurgency with big-war tactics, and lost. In reaction, the military and the public swore next time to fight even bigger, and did so, with success, against Iraq in 1991. Victory in Iraq and defeat in Vietnam combined to entrench the so-called Powell Doctrine: Don't fight unless you mobilize massively.

Although that doctrine has much to commend it, Boot's book suggests that it also throws a century or more of hard-won military wisdom out the window. The world today looks less like the 20th-century world, in which America confronted a few military juggernauts, than like the 19th-century world, in which America confronted troublemakers and failed states all over the place. In this new (old?) world, an allergy to small, aggressive deployments may be literally self-defeating.

And here is an eyebrow-raiser: There is nothing remotely new about wars without exit strategies, or wars in which American troops act as "nation builders" and "social workers." Until recently, Americans who intervened abroad generally expected to stick around and did so to good effect, building roads, hospitals, governments, and often goodwill. The United States has occupied Samoa, Wake Island, Cuba, Puerto Rico, the Philippines, Panama, Nicaragua, Veracruz, Haiti, the Dominican Republic, and the Virgin Islands, to say nothing of Germany and Japan. Many of these occupations were successful, and none was a quagmire. The Bush administration's reluctance to use U.S. forces to pacify Afghanistan may, in a few years, look like a sadly false economy.

The Pentagon, Boot notes, has recently begun to reconfigure itself for smaller wars. "The Air Force reorganized itself into expeditionary units. The Army set up an experimental medium-weight brigade designed to deploy anywhere in the world within 96 hours." The Marines even set about writing an updated "Small Wars Manual." "But the armed forces," writes Boot, "need to change more than their organizational chart; they need to change their outlook. Their mind-set remains that of a mass army composed of conscripts mobilized to win a big war, but that is not the role of the armed forces early in the 21st century."

What is that role? As you read this, teams of American soldiers are combing the badlands of Afghanistan (and possibly Pakistan) for Al Qaeda fighters and fugitives. Herman Hanneken would have understood. Even if U.S. forces in Afghanistan fail to get Osama bin Laden, the significance of their work there is large, because the wars they are relearning to fight are small.

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