Dec. 12, 2011 -- Eight years and four tours of duty later, Sgt. First Class Larry D. Green Jr. left Iraq for the final time this week.
"The joy is knowing this is a one-way trip," Green, 33, said. "It feels good to be out. ... As we crossed the border I smiled to myself. I said, 'I made it through to the end.'"
Nine years after a contentious, multibillion-dollar war, the United States is closing its bases in Iraq and bringing back combat troops. The U.S. withdrawal has caused rejoicing in both countries, even though the United States and Iraq face a new set of challenges as they work to figure out a way forward.
"After nearly nine years, our war in Iraq ends this month. ... A new day is upon us," President Obama said after his meeting today with Iraqi Prime Minister Nouri al-Maliki, who is in Washington, D.C. to discuss the two countries' future relationship.
Calling for the beginning of a "normal relationship" between the two countries, Obama hailed the beginning of a new chapter and reaffirmed the United States' "strong presence in the Middle East."
But the new chapter for both countries is filled with enormous challenges. Iraq continues to be rocked by Sunni-Shia, Kurdish-Iraqi violence and the absence of a strong, stable regime. For the United States, the growing influence of Iran on one border and Syria on the other is a continuing cause of concern.
"Iraq's in a tough neighborhood," Obama acknowledged.
It will be a difficult road ahead, some experts say, given the lack of direction on both fronts.
"It's obvious that we have to redefine our position in the rest of the Gulf and the region, but no one at present can figure out what our role should be," said Tony Cordesman of the Center for Strategic and International Studies. "The concept of having Iraq as a friendly, strong and democratic state is not a strategy. It's a goal. It's a goal which we have no plan as yet to meet."
The Iraq war has cost U.S. taxpayers more than $700 billion, with the monthly cost touching $4 billion. Nearly 4,500 Americans and 104,000 Iraqis have died since the war began, and more than 32,000 Americans have been wounded.
There are 5,500 U.S. troops in Iraq today, down from the peak of 170,000 in 2007.
In all likelihood, the United States will maintain a strong civil presence in the country and troops in neighboring countries such as Kuwait. But the direction of Iraq and the U.S. relationship remain hazy and neither of the two leaders today mentioned any specific steps they will take, except to say that there will be a "comprehensive partnership."
Maliki's "visit is little more than an exercise in political symbolism. It is celebrating a victory that really doesn't exist yet. While the war in the narrowest sense may be over, there is no end game here,"Cordesman said. "Given all the costs and the blood and the money, it's difficult to describe this as any kind of victory, particularly because when we went in, we destroyed Iraq's conventional forces, and they are years away from any meaningful recovery."
In both Iraq and the United States, here has been unanimous agreement on the ground that it's time for the U.S. troops to leave.
"We have given them all the tools and we've worked with them and trained them for years," said Army Staff Sgt. Farren Mathews, who has served three tours in Iraq. "It's up to them whether they move forward or not. Time for us to let them go and see what they do."
The 38-year-old said he hopes to never come back.
Iraqis also hailed the departure of the forces. In Fallujah, the scene of an alleged massacre in 2004 and a town where U.S. forces admitted to using white phosphorous, residents celebrated U.S. troops' departure.
"The withdrawal of Americans is a cause for celebration, very happy that Americans are leaving," one resident said. "Iraq is a prosperous, peaceful country. Iraqis are good people, and the U.S. had a negative effect on society."
Obama, who announced the end of the combat mission in Iraq in August 2010, has been careful to make it clear that this would not be a "victory lap."
"It is not going to be self-congratulatory," Obama said in a primetime speech last year. "There's still a lot of work that we got to do to make sure that Iraq is an effective partner for us."
Conservatives Assail Obama on Iraq Withdrawal
The withdrawal, which will be complete this month, fulfills a promise candidate Obama made in 2008 to pull out all troops from what he called a "dumb war."
Making his opposition to the war in Iraq a pivotal part of his campaign, candidate Obama promised to pull all U.S. combat troops out of the country by 2009.
"I opposed the war in Iraq before it began, and would end it as president," then-Sen. Obama wrote in a New York Times op-ed in 2008. "I believed it was a grave mistake to allow ourselves to be distracted from the fight against al Qaeda and the Taliban by invading a country that posed no imminent threat and had nothing to do with the 9/11 attacks."
Republicans have assailed Obama for pulling U.S. troops out of Iraq, with many saying it's too early.
"The meeting between President Obama and Prime Minister Maliki today cannot obscure the fact that both men have failed in their responsibilities with regard to our shared security interests," Sen. John McCain, R-Ariz., said in a statement. "All of the progress that both Iraqis and Americans have made, at such painful and substantial cost, has now been put at greater risk."
Virtually all 2012 candidates have criticized the president's decision. Former Massachusetts Gov. Mitt Romney called it a "failure to deliver."
Front-runner Newt Gingrich has blasted Obama for ushering in failure, even though he once said in a Newsweek interview that Americans can't win in Iraq.
Obama's supporters, however, charge that Republicans' criticism is bogus, especially because the Iraqi democratic government that the United States sought to create doesn't want troops to stay.
"They are on Mars," said Jon Stolz, founder of VoteVets who returned from duty in Iraq a week ago. "If the Republicans want to make it an issue they can, and they will lose on it. They are better off not talking about it."
ABC News' Luis Martinez contributed to this report.