Lt. Col. Mark Bieger huddled his infantrymen in a darkened parking lot minutes before they were to depart Baghdad for the last time.

"This is a historic mission!" he bellowed, struggling to be heard over the zoom of fighter jets and unmanned drones deployed to watch over the brigade's convoy to Kuwait. "A truly historic end to seven years of war."

The 4th Stryker Brigade, 2nd Infantry Division, which left Iraq this week, was the final U.S. combat brigade to be pulled out of the country, fulfilling the Obama administration's pledge to end the U.S. combat mission by the end of August. About 50,000 U.S. troops will remain in Iraq, mainly as a training force.

"Operation Iraqi Freedom ends on your watch!" exclaimed Col. John Norris, the head of the brigade.

"Hooah!" the soldiers roared, using an Army battle cry.

Shortly before midnight Saturday, a group of infantrymen boarded Stryker fighting vehicles, left an increasingly sparse base behind and began scanning the sides of a desolate highway for bombs. For many veterans, including some who made the same trip in the opposite direction years ago under fire, it was a fitting way to exit.

"They're leaving as heroes," Norris said of his soldiers. "I want them to walk home with pride in their hearts."

Besides pride, the soldiers will carry with them the hidden costs of war: hardened glares; tales of comrades' deaths relayed in monotone sentences devoid of emotion; young faces rendered incongruously old.

There might never be an acknowledged end to the Iraq war -- a moment where it ceases being America's conflict. U.S. commanders acknowledge that the months-long political impasse over the disputed March 7 elections and a flurry of other unresolved disputes in Iraq have the potential to erode hard-won security gains.

But U.S. commanders also seem to be stressing that this is no longer America's war to lose. "I will let history judge whether we reached irreversible momentum," Norris said. "That's not my call."

By the end of this month, the United States will have six brigades in Iraq, by far its smallest footprint since the 2003 invasion. Those that remain are conventional combat brigades reconfigured slightly and rebranded "advise and assist brigades." The primary mission of those units and the roughly 4,500 U.S. special operations forces that will stay behind will be to train Iraqi troops. Under a bilateral agreement, all U.S. troops must be out of Iraq by Dec. 31, 2011.

Leaving Iraq one last time is particularly emotional for veterans who have served multiple tours, several soldiers said in the two-day journey through the southern desert to Kuwait in cramped, windowless vehicles.