KORENGAL VALLEY, AFGHANISTAN -- It was as if the five years of almost ceaseless firefights and ambushes had been a misunderstanding -- a tragic, bloody misunderstanding.

More than 40 U.S. soldiers have been killed, and scores more wounded, in helicopter crashes, machine-gun attacks and grenade blasts in the Korengal Valley, a jagged sliver just six miles deep and a half-mile wide. The Afghan death toll has been far higher, making the Korengal some of the bloodiest ground in all of Afghanistan, according to U.S. and Afghan officials.

In the pre-dawn hours of Wednesday, the American presence here came to an abrupt end.

The day before, Capt. Mark Moretti, the 28-year-old commander of U.S. forces in the valley, walked two dozen Korengali elders around his base and told them that the United States was withdrawing. He showed the elders the battle-scarred American barracks; a bullet-ridden crane; wheezing generators and a rubber bladder brimming with 6,000 gallons of fuel.

Moretti, the son of a West Point physics professor, and Shamshir Khan, a valley elder whose son had been jailed for killing two U.S. soldiers, sat together on a small wall near the base's helicopter pad. In keeping with local custom among friends, they held hands.

Moretti gently reminded Khan of the deal they had reached a few days earlier: If U.S. troops were allowed to leave peacefully, the Americans wouldn't destroy the base, the crane and the fuel. Khan assured him that the valley's fighters would honor the deal.

"I hope that when I am gone you will do what is best for your valley and the villagers," an almost wistful Moretti said.

"I want you to travel safely to your home, to your family," the 86-year-old elder replied. He gazed at the American officer through thick glasses that magnified rheumy, brown eyes and beamed.

Over the previous week, hundreds of U.S. Army Rangers and Afghan commandos had pushed into the valley to control the high ground the enemy would need for a big attack on departing troops. Dozens of cargo helicopters hauled off equipment. By Wednesday morning, the last Americans were gone.

For U.S. commanders, the Korengal Valley offers a hard lesson in the limits of American power and goodwill in Afghanistan. U.S. troops arrived in 2005 to flush out al-Qaeda and Taliban fighters. They stayed on the theory that the American presence drew insurgents away from areas where the United States had a better chance of fostering development. The troops were, in essence, bullet magnets.

In 2010 a new set of commanders concluded that the U.S. had blundered into a blood feud with fierce and clannish villagers who wanted above all to be left alone. By this logic, subduing the Korengal wasn't worth the cost in American blood.

The retreat carries risks. Insurgents could use the Korengal as a haven to plan attacks in other parts of Afghanistan. The withdrawal could offer proof to other Afghans that American troops can be forced out.

The American hope is that pulling out of the Korengal rectifies a mistake and that Moretti's troops can be put to better use stabilizing larger, less violent areas where the U.S. presence is more tolerable and there is a greater desire for development.

"You can't force the local populace to accept you in their valley," Moretti said. "You can't make them want to work with us."

'A waste of time'

On April 7, Moretti and about three-dozen U.S. soldiers set out on foot for the town of Aliabad about one mile from the Korengal Outpost, the main U.S. base in the valley. Rumors of the American departure had begun spreading through the area and intelligence reports suggested that insurgent commanders were planning a large-scale attack on one of the three U.S. firebases in the area. Moretti was eager to find out what the valley's elders knew.

The U.S. troops walked down a dirt trail, scanning the ridgelines. About a half-mile from the U.S. outpost a bomb exploded at their feet, spraying shrapnel, shards of rock and dirt. Blood trickled from a 22-year-old soldier's blown eardrum, cutting a narrow path down his dirt-caked face.

"I can't hear a [expletive] thing," the soldier said. Another soldier suffered what appeared to be a broken leg.

"If you have eyes on the triggerman you are cleared to fire," Moretti screamed.

His troops blasted away at a lone figure running along the ridgeline on the other side of the valley. An attack helicopter fired a missile into an abandoned home where one of the soldiers thought he saw the triggerman.

The wounded were carried back to the base and evacuated by helicopter. Moretti and the rest of the patrol resumed their Korengal commute, heading to Aliabad in search of Khan and his younger brother-in-law Zalwar Khan.

Moretti and the elderly Afghans sat together on a small porch overlooking terraces of brilliant, emerald winter wheat. Shamshir Khan said little. The younger Khandid most of the talking. His role as the primary interlocutor between the Americans and the insurgents gave him a small measure of status. He had used his relationship with the American commanders to seek humanitarian aid for hungry villagers and cash payments for goats killed by U.S. mortar shells.

But Moretti had been boycotting weekly meetings of the elders and avoiding Zalwar Khan as a way to pressure them into greater cooperation. He also hoped that by ignoring Khan he could force him to build a relationship with Afghan government officials.

"You are the only American commander I have known who refuses to see me," Khan said in Pashto, his face just inches from Moretti's. "You are the only one who doesn't sit at the weekly shura. Why?"

"The shura is a waste of time," Moretti replied. "All we talk about is dead goats. In 10 months the meetings haven't accomplished a single thing."

He and Khan argued in circles for the next 15 minutes about whether villagers or outsiders were responsible for the violence in the valley before Moretti cut the conversation short.

"I know there are big plans for an attack on one of my bases," he said. "I want to hear about it." He told Khan that if the elder would give him information about the timing of the attack or the number of fighters in the valley he would return to the weekly shura.

Khan paused for a few seconds as if he were weighing the offer. "I don't know anything," he said.

An unbuilt road

Most of the Korengal's 4,000-5,000 residents live in stone houses that cling to they valley's steep walls. To survive they grow wheat and log towering cedars in defiance of a government ban on timber exports. They speak their own language.

For most of the past five years U.S. troops have exercised loose control over the first three miles of the valley. Beyond the three-mile mark, the insurgents have had free rein.

When he arrived in the Korengal last June, Moretti sent his troops into villages that hadn't seen a regular U.S. presence in a year. His plan was to drive the enemy back and persuade the elders to support a U.S.-funded effort to pave the sole road into the valley, a project that had stalled in 2007.

The road would connect the Korengal to the rest of eastern Afghanistan and in theory make it more governable. In September, as road construction was set to begin, insurgents killed six guards hired by the road contractor and took their weapons. The contractor quit.

Moretti's predecessors had spent countless hours trying to persuade Zalwar Khan to rally the locals to support the road. Three years of prodding had produced virtually no progress. Moretti sensed that the real power in the valley lay with the men leading the insurgency.

He asked Khan to deliver a letter to a timber baron and insurgent leader known as Matin, who like many Afghans uses only one name. Long before Moretti's arrival in the valley U.S. troops had killed several of Matin's family members in airstrikes, according to the Korengalis. In banning the timber trade, the Afghan government had deprived him of his sole means of income.

"Haji Matin hates the Americans too much," Khan told Moretti, using an honorific that signified Matin's completion of the pilgrimage to Mecca. "He won't respond."

Instead he advised Moretti to write to Nasurallah, a colleague of Matin's. "It is our belief that you are the rightful leader of the Korengalis," the captain wrote. "You hold the power not only among the villagers but also among the fighters. If you want the valley to prosper all you have to do is talk with us and bring your fighters down from the mountains."

The letter offered Nasurallah two choices: development or death. "It is not our wish to kill your fellow Korengalis," Moretti continued. "But we are good at it and will continue to do it as long as you fight us."

Two days later, Moretti received a response. "If you surrender to the law of God then our war against you will end," Nasurallah wrote. "If you keep fighting for man's law then we will fight you until Doomsday."

A change of ambition

Shortly after Gen. Stanley A. McChrystal took over as the top U.S. and NATO commander in Afghanistan last summer, he flew into the Korengal to meet with Moretti. At the time McChrystal was reluctant to pump any more troops into the stalemated fight. But he also was hesitant to leave out of concern that an American defeat in the Korengal would raise questions about American will and embolden other insurgents, U.S. officials said.

"Do you think you can turn the valley?" he asked Moretti, the son of one of his West Point classmates.

"I really believe we can make a difference," Moretti recalled telling him.

In the months since, Moretti and his commanders became increasingly convinced that the Korengalis' main ambition was to drive the Americans from the valley. They received training, money and weapons from supporters in Pakistan and the Middle East. But the Korengalis' fight was local.

"I don't believe there are any hardcore Taliban in the valley," said Lt. Col. Brian Pearl, who oversees U.S. military operations in the Korengal and a half dozen other valleys in eastern Afghanistan.

Last week McChrystal flew back into the valley. Moretti walked him through the plan to pull out his 154 troops. "Sir, I think we are looking forward to getting out of here," Moretti said. "I think leaving is the right thing to do."

Some of his soldiers were more blunt with the general. "This place is rough," said Pfc. Matthew Lunceford, who still had a gash across his cheek from the bombing on the way to see the Khans. "It is freaking nuts."

Moretti's troops had learned from earlier units' experience how to survive in the valley. They knew which ambush sites to avoid. They also patrolled areas that hadn't seen a U.S. presence in years in an effort to keep the enemy off balance.

In 10 months the unit lost only two soldiers. One sergeant committed suicide. The company's only combat fatality came in January when a platoon was ambushed while walking down an outdoor, stone stairway below Aliabad.

Spec. Robert Donevski, a 19-year-old from Sun City, Ariz., jumped a fence and opened fire on the enemy so that his fellow soldiers could scramble to safety. As he was climbing back over the fence to join his squad, a bullet struck him in the head. He died at an Army field hospital.

Moretti mourned the losses. He also recognized that losing just two soldiers in 10 months in the Korengal was a victory.

"In this place, with all its violent history, that is our proudest achievement," he said.