The war cost nearly 4,500 American and well more than 100,000 Iraqi lives and $800 billion from the U.S. Treasury. The question of whether it was worth it all — or whether the new government the Americans leave behind will remain a steadfast U.S. ally — is yet unanswered.

The 5-hour drive by the last convoy of MRAPS, heavily armored personnel carriers, took place under cover of darkness and under strict secrecy to prevent any final attacks on the withdrawing troops. The 500 soldiers didn’t even tell their Iraqi partners they were leaving before they slipped out of the last American base and started down the barren desert highway to the Kuwaiti border before dawn Sunday.

The atmosphere was subdued inside one of the vehicles as it streamed down the highway, with little visible in the blackness outside through the MRAP’s small windows. Along the road, a small group of Iraqi soldiers waved to the departing American troops.

"My heart goes out to the Iraqis," said Warrant Officer John Jewell, acknowledging the challenges ahead. "The innocent always pay the bill."

But after crossing the berm at the Kuwaiti border, lit with floodlights and ringed with barbed wire, the troops from the 3rd brigade of the Army’s 1st Cavalry Division were elated. They cheered, pumped fists in the air and gave each other chest bumps and bear hugs. "We’re on top of the world!" shouted one soldier from the turret of his vehicle.

"It’s just an honor to be able to serve your country and say that you helped close out the war in Iraq," said Spc. Jesse Jones, a 23-year-old who volunteered to be in the last convoy. "Not a lot of people can say that they did huge things like that that will probably be in the history books."

Spc. Brittany Hampton joked that no one was going to believe her back home when she told them she was in the very last of the 110 vehicles in the convoy to exit.

"But we really truly were the last soldiers in Iraq. So it’s pretty awesome," she said.

The quiet withdrawal was a stark contrast to the high-octane start of the war, which began before dawn on March 20, 2003, with an airstrike in southern Baghdad where Saddam Hussein was believed to be hiding, the opening shot in the famed "shock and awe" bombardment. U.S. and allied ground forces then stormed from Kuwait across the featureless deserts of southern Iraq toward the capital.

Saddam and his regime fell within weeks, and the dictator was captured by the end of the year — to be executed by Iraq’s new Shiite rulers in 2006. But Saddam’s end only opened the door to years more of conflict as Iraq was plunged into a vicious sectarian war between its Shiite and Sunni communities. The near civil war devastated the country, and its legacy includes thousands of widows and orphans, a people deeply divided along sectarian lines and infrastructure that remains largely in ruins.

In the past two years, violence has dropped dramatically, and Iraqi security forces that U.S. troops struggled for years to train have improved. But the sectarian wounds remain unhealed. Even as U.S. troops were leaving, the main Sunni-backed political bloc announced Sunday it was suspending its participation in parliament to protest the monopoly on government posts by Shiite allies of Prime Minister Nouri al-Maliki.

President Barack Obama stopped short of calling the U.S. effort in Iraq a victory in an interview taped Thursday with ABC News’ Barbara Walters.

"I would describe our troops as having succeeded in the mission of giving to the Iraqis their country in a way that gives them a chance for a successful future," Obama said.

In the final days, U.S. officials acknowledged the cost in blood and dollars was high, but tried to paint a picture of victory — for both the troops and the Iraqi people now freed of a dictator and on a path to democracy. But gnawing questions remain: Will Iraqis be able to forge their new government amid the still stubborn sectarian clashes? And will Iraq be able to defend itself and remain independent in a region fraught with turmoil and still steeped in insurgent threats?

"We are glad to see the last U.S. soldier leaving the country today. It is an important day in Iraq’s history, but the most important thing now is the future of Iraq," said 25-year-old Said Hassan, the owner of money exchange shop in Baghdad.

"The Americans have left behind them a country that is falling apart and an Iraqi army and security forces that have a long way ahead to be able to defend the nation and the people."

Some Iraqis celebrated the exit of what they called American occupiers, neither invited nor welcome in a proud country. Others said that while grateful for U.S. help ousting Saddam, the war went on too long. A majority of Americans would agree, according to opinion polls.

Iraq’s military chief of staff, Lt. Gen. Babaker Zebari said Sunday that his troops were up to the task of uprooting militant groups. Sunni militants continue to carry out bombing and shooting against police, soldiers and civilians, and Shiite militias continue to operate.

"There are only scattered terrorists hiding here and there and we are seeking intelligence information to eliminate them," Zebari said. "We are confident that there will be no danger."

The U.S. convoys Sunday were the last of a massive operation pulling out American forces that has lasted for months to meet the end-of-the-year deadline agreed with the Iraqis during the administration of President George W. Bush.

As of Thursday, there were two U.S. bases and less than 4,000 U.S. troops in Iraq — a dramatic drop from the roughly 500 military installations and as many as 170,000 troops during the surge ordered by Bush in 2007, when violence was at its worst. As of Saturday night, that was down to one base — Camp Adder — and the final 500 soldiers.

On Saturday evening at Camp Adder, near Nasiriyah, about 200 miles southeast of Baghdad, the vehicles lined up in an open field to prepare and soldiers went through last-minute equipment checks to make sure radios, weapons and other gear were working.

Gen. Lloyd Austin, the commanding general for Iraq, walked through the rows of vehicles, talking to soldiers over the low hum of the engines. He thanked them for their service and reminded them to stay vigilant on their final mission.

"I wanted to remind them that we have an important mission left in the country of Iraq. We want to stay focused and we want to make sure that we’re doing the right things to protect ourselves," Austin said.

The commander of the Special Troops Battalion, Lt. Col. Jack Vantress told his soldiers, "We are closing the book on an operation that has brought freedom to a country that was repressed. When the sun comes up, we’ll be across the berm."

He added a warning to watch out for any final attacks. "Laser focus. Laser focus. You’ve got time, hours of road to go. There are people out there who still want to hurt you."

Early Saturday morning, the brigade’s remaining interpreters made their routine calls to the local tribal sheiks and government leaders that the troops deal with, so that they would assume that it was just a normal day.

"The Iraqis are going to wake up in the morning and nobody will be there," said Spc. Joseph, an Iraqi American who emigrated from Iraq in 2009 and enlisted. He asked that his full name be withheld to protect his family.

In a guard tower overlooking a now empty checkpoint at the base, Sgt. Ashley Vorhees and another soldier talked about what they looked forward to most in getting home. The 29-year-old Vorhees planned to go for Mexican food at Rosa’s, a restaurant in Killeen, Texas. Another joy of home, she said: you don’t have to bring your weapon when you go to the bathroom.

At its height, Camp Adder boasted a Taco Bell, a KFC, an Italian restaurant and two Green Beans coffee shops. On Saturday, it felt empty, with abandoned volleyball and basketball courts and a gym called "House of Pain." Hundreds of vehicles — trucks, buses — waited in a lot to be handed over to the Iraqi military, which is taking over the site. With the Americans gone, the base reverts to its former name, Imam Ali Air Base.

Despite Obama’s earlier contention that all American troops would be home for Christmas, at least 4,000 forces will remain in Kuwait for some months. The troops could also be used as a quick reaction force if needed.

The U.S. plans to keep a robust diplomatic presence in Iraq, hoping to foster a lasting relationship with the nation and maintain a strong military force in the region. Obama met in Washington with Prime Minister al-Maliki last week, vowing to remain committed to Iraq as the two countries struggle to define their new relationship.

U.S. officials were unable to reach an agreement with the Iraqis on legal issues and troop immunity that would have allowed a small training and counterterrorism force to remain. U.S. defense officials said they expect there will be no movement on that issue until sometime next year.

Capt. Mark Askew, a 28-year-old from Tampa, Florida who was among the last soldiers to leave, said the answer to the question of whether the Iraq war was worth the cost will depend on what type of country and government Iraq ends up with years from now, whether they are democratic, respect human rights and are considered an American ally.

"It depends on what Iraq does after we leave," he said, speaking before the final convoy departed. "I don’t expect them to turn into South Korea or Japan overnight."