BAGHDAD - The last convoy of US soldiers pulled out of Iraq on Sunday, ending their withdrawal after nearly nine years of war and military intervention that cost almost 4,500 American and tens of thousands of Iraqi lives.

The war launched in March 2003 with missiles striking Baghdad to oust Saddam Hussein is leaving behind a fragile democracy still facing insurgents, sectarian tensions and a struggle to define its place in the Arab region.

US Air Force airman wait to board the last Air Force flight out of Ali Air Base near Nasiriyah, en route to Kuwait Dec 17, 2011. [Photo/Agencies]

The final column of around 100 mostly US military MRAP armoured vehicles carrying 500 US troops trundled across the southern Iraq desert through the night along an empty highway to the Kuwaiti border.

"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, 300 km (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."    

For President Barack Obama, the military pullout is the fulfilment of an election promise to bring troops home from a conflict inherited from his predecessor that tainted America's standing worldwide.

For Iraqis, it brings a sense of sovereignty but fuels worries their country may slide once again into the kind of sectarian violence that killed thousands of people at its peak in 2006-2007.

Prime Minister Nuri al-Maliki's Shi'ite-led government still struggles with a delicate power-sharing arrangement between Shi'ite, Kurdish and Sunni parties, leaving Iraq vulnerable to meddling by Sunni Arab nations and Shi'ite Iran.

The intensity of violence and suicide bombings has subsided for now. But a stubborn Sunni Islamist insurgency and rival Shi'ite militias remain a threat, carrying out almost daily attacks.

Iraq says its forces can contain the violence but they lack capabilities in areas such as air defence and intelligence gathering. A deal for several thousand US troops to stay on as trainers fell apart over the sensitive issue of legal immunity.

For many Iraqis security remains a worry - but no more than jobs and getting access to power in a country whose national grid provides only a few hours of electricity a day.

"We don't think about America... We think about electricity, jobs, our oil, our daily problems," said Abbas Jaber, a government employee in Baghdad. "They left chaos."