The American military reinvented itself to fight insurgencies during the decade of combat that began with an onslaught against the Taliban 10 years ago Friday.

Having focused so narrowly - and spent so heavily - on fighting insurgents and terrorists rather traditional armies, navies and air forces, U.S. military leaders are eager to turn to a wider range of threats, including potential conflict with China. They will have less money at hand, but they do possess a battle-seasoned force dominated by soldiers who have never served in peacetime and commanders who learned the hard way that the next battle never looks the same as the last one.

In both Iraq and Afghanistan, the military has operated virtually unchallenged in the air. Nor has it faced large-scale missile attacks or cyberthreats. Instead it was challenged by improvised roadside bombs, kidnappings and propaganda assaults. Looking ahead, strategists see a different set of threats, particularly from a Chinese military that is modernizing air and naval forces and posing a potential menace to U.S. dominance in space.

As an illustration of how long the military has been continuously at war, the F-14 Tomcat fighters that helped launch the American-led invasion four weeks after the Sept. 11, 2001, terrorist attacks have been retired for the past five years. And the aircraft carrier from which they flew, the USS Enterprise, is to be retired in 2013, one year before U.S. and NATO troops are to hand the war's lead role to Afghan forces.

A pivot to the threats of the future will require reorienting the way the military trains and plans, and maybe how and what it buys.

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Complicating this effort, to an extent not foreseen even six months ago, is the likelihood of big reductions in the defense budget.

It now seems certain that the military will shrink, and so, too, may the ambitions of the national defense strategy it will be expected to execute.

The war in Afghanistan, combined with even more intense years of combat in Iraq, put strains on the U.S. military that will ease only gradually. As they do, the push to cut defense spending is likely to generate super-heated competition among the four major services. The smallest, the Marines, already are campaigning to recalibrate their role as a seafaring "expeditionary" force, and the Air Force and Navy are collaborating on a new doctrine, known as "Air Sea Battle," to define how they intend to operate together more effectively in the Asia-Pacific region.

The Army is eagerly awaiting a postwar respite from the rigors of repeated deployments for ground troops. But the largest service is feeling pressure to adapt. For most of the past decade it has focused mainly on countering insurgencies in Iraq and Afghanistan. The pace was so fast that Army leaders had little time to think beyond those battles, and soldiers enjoyed little time between combat tours.

"We're a tired Army," Gen. Richard Cody, a retired former Army vice chief of staff, told a House committee on Tuesday. American ground forces - both the Army and the Marine Corps - are "worn thin," he said, and should be spared sharp budget cuts.

Lt. Gen. Mark Hertling, the Army's top commander in Europe, put it this way: "We are an Army whose systems need to be polished. They've rusted." By that he meant, for example, that the Army needs to improve how it manages training and disciplines soldiers. While misbehavior is not widespread, he said, it has become a problem that demands fixing. Left long unattended, he said, it could become "cancerous."

The Afghanistan war has taken a toll on the Army in other, narrower, ways. Gen. David McKiernan, who made his mark as a commander in the early years of the Iraq war, was sacked as the top commander in Afghanistan in 2009 with the war going badly. Barely a year later his successor, Gen. Stanley McChrystal, who was widely seen as one of the Army's brightest stars, was forced out in a flap over comments in a magazine article.

The U.S. now has about 98,000 troops in Afghanistan. Under a plan announced by President Barack Obama in July, 10,000 will come home by the end of this year and 23,000 more by September 2012. Gradually, they intend to hand over security duties to the Afghans, who, despite a decade of training by U.S. and NATO troops, still lack much of the capability and expertise needed to prevent a return to power by the Taliban.

For several years, during the worst period of the Iraq war, the fighting in Afghanistan seemed secondary and casualties gained relatively little attention in the U.S. But in 2009 that began to change, as reflected by the fact that two-thirds of the almost 1,700 U.S. deaths in Afghanistan have happened since then.

The U.S. military will not leave Afghanistan abruptly, if current plans hold. Marine Gen. John Allen, the top U.S. and NATO commander in Kabul, said recently that although the Afghans will take the lead for security by the end of 2014, "We're going to be here a long time." The Obama administration has vowed not to abandon the Afghans, as the U.S. did after it helped anti-communist guerrillas oust Soviet forces in 1989.

Even so, attention is turning to postwar priorities.

Navy Adm. Mike Mullen, in his farewell remarks as chairman of the Joint Chiefs of Staff on Sept. 30, said the urgency of fighting in Iraq and Afghanistan left some worrisome soft spots in the military.

"We have become the best counterinsurgency force in the world, but we have done so at the expense of critical conventional capabilities we necessarily let lapse," he said.

"We have become the most expeditionary force in our history but in the process sacrificed some of the basics of garrison leadership and continuity that preserve the health of our all-volunteer force."