When the first U.S. military convoy rolled into 8-year-old Saad Kareem's middle class neighborhood in Baghdad nearly a decade ago, he was scared, even as others around him whistled and danced.

Saad's family is Shiite, and the U.S. invasion brought hope for political and religious freedoms they'd missed under Saddam Hussein's Sunni-dominated regime.

"I was with my mother at the time, holding my mother's hand very tight. I was so scared because I thought that they were coming to kill us," recalled Saad, now 17. "But when I saw my mother smiling, I relaxed."

The safety Saad felt in that moment proved elusive: First there was war, then sectarian strife that pitted Sunni extremists against Shiite militants and brought Iraq to the brink of civil war.

Then came the official end of the war. On December 31, 2011, the country celebrated "Iraq Day" and the departure of U.S. troops. As Iraq prepares to mark the anniversary, also known as the "Day of Sovereignty," last year's celebratory tone has been replaced by a more somber one.

Prime Minister Nuri al-Maliki's political bloc, the Islamic Dawa Party, called on Iraqis not to become divided along sectarian or ethnic lines by "malicious schemes." The country has struggled to define itself, as its government stumbles from one political crisis to another.

Just as the last U.S. troops withdrew, al-Maliki, a Shiite, moved to arrest Vice President Tariq al-Hashimi, a Sunni, who al-Maliki accused of using his security detail as a hit squad.

More recently, a few days before the first Iraq Day anniversary, thousands of Sunnis took to the streets in Anbar province, a major trade thoroughfare to Jordan and Syria, to protest al-Maliki's order to arrest the bodyguards of Finance Minister Rafaie Esawi, a Sunni. The arrest of Esawi's bodyguards came just hours after President Jalal Talabani, a Kurd who is widely viewed as a stabilizing political force in Iraq, left the country to undergo treatment for cancer in Germany.

Iraq's Arab Sunnis and Kurds have accused al-Maliki and his Shiite political party of working to consolidate power in Iraq by cutting them out of the political process, an allegation that comes as U.S. lawmakers raise concerns about Iraq strengthening its ties with Shiite-dominated Iran.

One year after U.S. troops left, much about a post-war Iraq remains unclear -- for the Iraqis recovering from war, and still facing bombs and battles; for Americans re-adjusting to life in the United States and wondering whether their work was worthwhile.

This time last year, there was cautious optimism among Saad's family members. It seemed possible the political instability and violence that plagued Iraq might ebb. In its place, Saad's family hoped a safer, more stable Iraq would emerge.

Today, at Saad's all-male high school in central Baghdad, talk routinely centers on the latest bombing or bubbling sectarian tensions -- Sunni versus Shiite, Arab versus Kurd. There are concerns, Saad said, about the possible return of al Qaeda in Iraq, a group of primarily Sunni extremists bent on reigniting sectarianism. The latest political crisis is split along sectarian lines and has raised fears that political strife could translate into violence on the streets.

Even with a dramatic decline in violence in Iraq from the height of the war, bombings and gun battles remain a near-daily occurrence. A car bomb killed Saad's best friend, and he's no longer allowed to walk to school. His father drives him instead.

Saad has vowed after graduating high school, he will leave Iraq. For good.

"Sometimes," Saad said, "I ask myself why God did not create me in another country."

'I don't think ... I really understood it'

U.S. Army Spec. Brittany Hampton looked out the window of the armored vehicle as it rolled down the highway.

Somehow, it was fitting that the 22-year-old woman who had seen her father off for the start of the Iraq war almost nine years earlier would be among the very last soldiers in the very last vehicle in the very last convoy to leave the country.

"I don't think that day I really understood it," she said nearly a year later.

Hampton, a medic, knew crossing from Iraq into Kuwait meant the end of the war for her and her fellow soldiers. But the historic nature of the moment hit her months later, when she was standing in front of the vehicle nicknamed "Praetorian 7" for the elite Roman guard unit that once protected Roman emperors.