It was a solemn, low-key ceremony outside a terminal at Baghdad's airport in a fortified area surrounded by concrete barriers.

　　U.S. Defense Secretary Leon Panetta flew in briefly for the ceremony, which was held in front of scores of U.S. troops and foreign media. There was a seat reserved for Iraqi Prime Minister Nouri al-Maliki. But he did not attend.

　　Soldiers took the flag representing the U.S. military command in Iraq, rolled it around the staff, and slipped into a camouflage cloth case. The gesture marked the symbolic end of Operation New Dawn and the war that lasted nearly nine years, killed more than 4,000 Americans along with tens of thousands of Iraqis, and unleashed sectarian violence in the country.

　　Panetta called’s Thursday’s ceremony a historic occasion. "To be sure, the cost was high, in blood and treasure for the United States and for the Iraqi people. Those lives were not lost in vain," he said. "They gave birth to an independent, free and sovereign Iraq."

　　What U.S. forces leave behind is a stability that is fragile at best. Violence has diminished in the past few years, but continues to flare, with attacks carried out by insurgents, some of them operating with Iranian support.

　　Some U.S. officials had wanted to keep several thousand troops in place beyond a December 31 deadline that Washington and Baghdad set three years ago. However, President Obama announced a total withdrawal in October after his administration failed to reach an agreement for Iraq to provide immunity to U.S. troops.

　　At the time of the announcement, there were about 50,000 troops in Iraq. That number is down to a few thousand as the last convoys of trucks make their way south to bases in Kuwait.

　　In his remarks Thursday, Panetta said Washington will remain engaged in Iraq.

　　“Let me be clear," said Panetta. "Iraq will be tested in the days ahead by terrorism and by those who would seek to divide it; by economic and social issues; by the demands of democracy itself. Challenges remain, but the U.S. will stand by the Iraqi people as they navigate those challenges to build a stronger and more prosperous nation.”

　　The American embassy in Baghdad houses the United States’ largest diplomatic presence in the world, and a small number of troops will remain, mainly to protect diplomats.

　　Some Iraqis this week celebrated the departure of U.S. troops, while others expressed concern that the country could again slip into chaos and violence.

　　Whatever the outcome, the future of Iraq remains in the hands of its people.