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'A new chapter': US officially ends Iraq war

A ceremony held in Baghdad marked the official end of the nearly 9-year military campaign in Iraq, and now the 4,000 remaining troops in the country are heading home for the holidays. NBC's Richard Engel reports.

Updated at 6:10 p.m. ET

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.

Iraqi citizens offered a more pessimistic assessment. "The Americans are leaving behind them a destroyed country," said Mariam Khazim of Sadr City. "The Americans did not leave modern schools or big factories behind them. Instead, they left thousands of widows and orphans."

The Iraq Body Count website says more than 100,000 Iraqis have been killed since the U.S. invasion. The vast majority were civilians.

Updated at 10:58 a.m. ET

BAGHDAD --  U.S. forces formally ended their nine-year war in Iraq with a low-key flag ceremony in Baghdad on Thursday.

"After a lot of blood spilled by Iraqis and Americans, the mission of an Iraq that could govern and secure itself has become real," Defense Secretary Leon Panetta said at the ceremony at Baghdad's still heavily fortified airport.

Almost 4,500 U.S. soldiers and tens of thousands of Iraqis lost their lives in the war that began with a "Shock and Awe" campaign of missiles pounding Baghdad and descended into sectarian strife and a surge in U.S. troop numbers.

U.S. soldiers lowered the flag of American forces in Iraq and slipped it into a camouflage-colored sleeve in a brief outdoor ceremony, symbolically ending the most unpopular U.S. military venture since the Vietnam War of the 1960s and 70s.

Iraqi Prime Minister Nouri al-Maliki and President Jalal Talabani were invited to the ceremony but did not attend.

In addition to the dead, the war left 32,000 Americans wounded and cost the U.S. more than $800 billion.

The remaining 4,000 American troops will leave by the end of the year.

Bombings are still common. Experts are also concerned about the Iraqi security force's ability to defend the nation against foreign threats.

However, Panetta said veterans of the conflict can be "secure in knowing that your sacrifice has helped the Iraqi people to cast tyranny aside."

Some Iraqi citizens offered a more pessimistic assessment. "The Americans are leaving behind them a destroyed country," said Mariam Khazim of Sadr City. "The Americans did not leave modern schools or big factories behind them. Instead, they left thousands of widows and orphans."

Gen. Lloyd Austin, the top U.S. commander in Iraq, and Army Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, also spoke during the ceremony.

Updated at 5:46 a.m. ET: Austin says Iraqis now have "unprecedented opportunities."

Sen. John McCain, the ranking Republican member of the Senate Armed Services Committee, discusses the withdrawal of U.S. troops from Iraq with TODAY's Matt Lauer. McCain says we risk losing everything we gained in the war-torn country by not leaving a residual force behind, apart from about 200 military advisers.

Updated at 5:42 a.m ET: "Since 2003, we have helped the Iraqi security forces grow from zero to 650,000-strong," Austin says.

Updated at 5:40 a.m. ET: Austin recalls how he was present when American forces secured the airfield where the ceremony is being held. "After 21 days of tough fighting, we ended Saddam Hussein's reign of terror," he adds.

Updated at 5:37 a.m. ET: Army Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, points out that the next time he visits Baghdad it will have to be at the invitation of the Iraqi government. "I kinda like that," he adds.

Updated at 5:32 a.m. ET: "This is not the end, this is the beginning," Panetta says. "May God bless Iraq, its people and its future."

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U.S. troops take part in the end of mission ceremony in Baghdad, Iraq, on Thursday.

Updated at 5:29 a.m. ET: "Let me be clear, Iraq will be tested in the days ahead -- by terrorism, by those who would seek to divide," Panetta says. "Challenges remain but the United States will be there to stand with the Iraqi people. We are not about to turn our backs on all that has been sacrificed and accomplished."

Updated at 5:26 a.m. ET: "Your sacrifice has helped the Iraqi people begin a new chapter in history, free from tyranny," Panetta says. "This outcome was never certain, particularly during the war's darkest days."

Updated at 5:23 a.m. ET: Panetta highlights the "heartbreak" of military families who watched their loved ones go off to war.

Updated at 5:18 a.m. ET: "It is a profound honor to be here in Baghdad," Panetta says at ceremony."No words, no ceremony can provide full tribute to the sacrifices that have brought this day to pass."

Saddam's Iraq is gone, but in its place is a state with close ties to one of America's biggest and most unpredictable enemies: Iran. NBC's Richard Engel has been covering the war from the start, and went back for this historic week to take a closer look at the Iran connection.

Updated at 5:16 a.m. ET: "We look forward to an Iraq that is sovereign, secure and self-reliant," US Ambassador to Iraq James Jeffrey says.

Published at 4:45 a.m. ET: After nearly nine years, 4,500 American dead, 32,000 wounded and more than $800 billion, U.S. officials prepared Thursday to formally shut down the war in Iraq — a conflict that U.S. Defense Secretary Leon Panetta said was worth the price in blood and money, as it set Iraq on a path to democracy.

Panetta stepped off his military plane in Baghdad Thursday as the leader of America's war in Iraq, but will leave as one of many top U.S. and global officials who hope to work with the struggling nation as it tries to find its new place in the Middle East and the broader world.

He and several other U.S. diplomatic, military and defense leaders will participate in a highly symbolic ceremony during which the flag of U.S. Forces-Iraq will officially be retired, or "cased," according to Army tradition.

During several stops in Afghanistan this week, Panetta made it clear that the U.S. can be proud of its accomplishments in Iraq, and that the cost of the bitterly divisive war was worth it.

After nearly nine years and 4,500 American lives lost, President Obama and the first lady officially marked the end of the Iraq war Wednesday. NBC's Kristen Welker has more.

"We spilled a lot of blood there," Panetta said. "But all of that has not been in vain. It's been to achieve a mission making that country sovereign and independent and able to govern and secure itself."

That, he said, is "a tribute to everybody — everybody who fought in that war, everybody who spilled blood in that war, everybody who was dedicated to making sure we could achieve that mission."

Panetta has echoed President Barack Obama's promise that the U.S. plans to keep a robust diplomatic presence in Iraq, foster a deep and lasting relationship with the nation and maintain a strong military force in the region.

As of Thursday, there were two U.S. bases and about 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 President George W. Bush in 2007, when violence and raging sectarianism gripped the country. All U.S. troops are slated to be out of Iraq by the end of the year, but officials are likely to meet that goal a bit before then.

Read more about the Iraq withdrawal

The total U.S. departure is a bit earlier than initially planned, and military leaders worry that it is premature for the still maturing Iraqi security forces, who face continuing struggles to develop the logistics, air operations, surveillance and intelligence sharing capabilities they will need in what has long been a difficult neighborhood.

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.

Jon Soltz of VoteVets.org and Matthew Hoh of the Center for International Policy debate the winners and losers of the Iraq War and the non-military presence that will remain.

Still, 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 will be able to help finalize the move out of Iraq, but could also be used as a quick reaction force if needed.

Bombings and attacks have eased since American and Iraqi security forces weakened insurgents. But roadside bombs, car bombs and assassinations still kill and maim almost every day.

A frail economy, constant power shortages, scarce jobs and discontent with political leaders all fuel uncertainty among Iraqis.

"Thanks to the Americans. They took us away from Saddam Hussein, I have to say that. But I think now we are going to be in trouble," said Malik Abed, 44, a vendor at a Baghdad fish market. "Maybe the terrorists will start attacking us again."

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The Associated Press, Reuters, NBC News and msnbc.com staff contributed to this report.