A soldier crosses the border into Kuwait, August 2010. (U.S. Army/Flickr)

The U.S. military officially declared the end of the mission Dec. 15, following through on President Barack Obama's end-of-year deadline announced on Oct. 21.

From NBC World News:

The Iraq war began on March 20, 2003, at a time when national defense was a top priority for Americans still shocked by the Sept. 11, 2001, terrorist attacks. It continued with the invasion and ouster of Saddam Hussein, then ground through years of war against an insurgency that left tens of thousands dead.

Among those dead were nearly 4,500 Americans, and the war cost $800 billion from the U.S. Treasury. The question of whether it was worth it all is yet unanswered.

"It's good to see this thing coming to a close. I was here when it started," Staff Sgt. Christian Schultz said just before leaving Contingency Operating Base Adder, 185 miles south of Baghdad, for the border. "I saw a lot of good changes, a lot of progress, and a lot of bad things too."

See a comprehensive list of other important dates in the Iraq war here, compiled by the Associated Press.

According to NPR, Contingency Operating Base Adder in southern Iraq was a main staging ground for troops slated to leave the country, and was the last U.S. base to close. The last convoy composed of 500 soldiers crossed the border into Kuwait around daybreak on Sunday. But the "end of days" was not without a degree of unease.

From NPR:

Gen. Lloyd Austin, who commanded all U.S. troops in Iraq, says he was also worried about roadside attacks as the troops pulled out. He flew down to COB Adder for the last casing of the colors, when the army division's flag is put into its case and sent back home to the U.S.

This war is not like other wars that have ended with the signing of treaties or an exit from friendly territory, Austin says. One American base not far from COB Adder recently had 47 rocket attacks in a single day.

Pulling tens of thousands of troops out in this kind of environment is a logistical marvel, he says.

"You're reposturing while people are still trying to cause you harm," Austin says. "That means that every element that moves has to be protected. It is the most difficult undertaking in our lifetime, in our military career."

While few are willing to trivialize the milestone as a political move in the upcoming presidential election, NBC also pointed out for Obama, the withdrawal is "the fulfillment of tan election promise to bring troops home from a conflict inherited from his predecessor that tainted America's standing worldwide."

U.S. troops leave the country with a sense of independence, but a palpable vulnerability. Concerns of sectarian violence abound as Iraq looks now to preserve the precarious governing balance between Shiite, Kurdish and Sunni parties. According to U.S. officials, about 16,000 people will serve as diplomats, federal workers and contractors to ease into the transition, and talks could resume next year regarding future U.S. training missions.

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