The last convoy of U.S. soldiers pulled out of Iraq on Sunday, ending nearly nine years of war that cost over one million Iraqi and 4,500 American lives and left the Middle Eastern country grappling with extremism, sectarianism and terrorism. 

According to the California-based investigative organization Project Censored, more than one million Iraqis have been killed in the U.S.-led invasion and subsequent occupation of the country since March 2003. 

Washington said the military action was carried out to discover the weapons of mass destruction (WMD) when former dictator Saddam Hussein's Baathist regime was in power. However, no WMDs have ever been found in Iraq. 

Under a 2008 bilateral security accord, known as the Status of Forces Agreement (SOFA), all the troops are required to leave the country by December 31. 

The final column of around 100 mostly U.S. military MRAP armored vehicles carrying 500 U.S. troops trundled across the southern Iraq desert from their last base through the night and daybreak along an empty highway to the Kuwaiti border, Reuters reported.

Honking their horns, the last batch of around 25 American military trucks and tractor trailers carrying Bradley fighting vehicles crossed the border early Sunday morning, their crews waving at fellow troops along the route.

“I just can't wait to call my wife and kids and let them know I am safe,” Sgt. First Class Rodolfo Ruiz said as the border came into sight. Soon afterwards, he told his men the mission was over, “Hey guys, you made it.”

For U.S. President Barack Obama, the military pullout is the fulfillment of an election promise to bring troops home from a conflict inherited from his predecessor, the most unpopular war since Vietnam and one that tainted America's standing worldwide.

For Iraqis, though, the U.S. departure brings a sense of sovereignty tempered by nagging fears their country may slide once again into the kind of sectarian violence that killed many thousands of people at its peak in 2006-2007.

The intensity of violence and suicide bombings has subsided. But a stubborn Sunni insurgency and rival militias remain a threat, carrying out almost daily attacks, often on Iraqi government and security officials.

Iraq says its forces can contain the violence but they lack capabilities in areas such as air defense and intelligence gathering. A deal for several thousand U.S. 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 despite the OPEC country's vast oil potential.

U.S. and foreign companies are already helping Iraq develop the world's fourth-largest oil reserves, but its economy needs investment in all sectors, from hospitals to infrastructure.

“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 (Americans) left chaos.”

After Obama announced in October that troops would come home by the end of the year as scheduled, the number of U.S. military bases was whittled down quickly as hundreds of troops and trucks carrying equipment headed south to Kuwait.

U.S. forces, which had ended combat missions in 2010, paid $100,000 a month to tribal sheikhs to secure stretches of the highways leading south to reduce the risk of roadside bombings and attacks on the last convoys.

Only around 150 U.S. troops will remain in the country attached to a training and cooperation mission at the huge U.S. embassy on the banks of the Tigris river.

At the height of the war, more than 170,000 U.S. troops were in Iraq at more than 500 bases. By Saturday, there were fewer than 3,000 troops, and one base - Contingency Operating Base Adder, 300 km (185 miles) south of Baghdad.