It began with shock and awe and ended with a silent trickle across the border in the dead of night. As the 4th Stryker Brigade, Second Infantry division, arrived at their staging post in the sands of Kuwait, Sergeant Donald Wilms got out of his battle truck and high-fived friends in his platoon. A few hours earlier they had rumbled across the dusty border, becoming the last US combat unit to leave Iraq.

"We knew we were going to make history," he said. "The whole platoon is extremely proud of the difference they were able to make."

Two trucks in front of him, Staff Sergeant Wiley Baker also had a sense of the moment. "Any time in a war, whether it be world war two or Vietnam, the first and the last in are setting the agenda," he said. "We were glad to be a part of it."

For the men and women of the division, seven years and five months of war in Iraq is now over. As soon as they had crossed the border after a three-day drive along the spine of central Iraq, US commanders announced that the overall American combat mission in the country was also complete – 12 days earlier than the official end of operations and with doubts about the continuing US role in Iraq lingering.

The soldiers had driven for about 18 hours south from Baghdad, along Route Tampa – the road the US army and marines had used to get to Baghdad in 2003. Now they were using it to leave.

They had moved mostly at night to lessen the risk of roadside bombs and ambushes along the main highway south – a vast, flat thoroughfare that had been built by Saddam, literally to move armies. As central Iraq convulsed in violence from 2005-08, the highway had become almost a no-go zone for civilians.

Just before the final drive over the border, Lieutenant Colonel Mike Lawrence stood bathed in the glow of a lamp tower, readying his remaining charges in the crunching gravel of a staging yard 100 miles north of the border. His young battalion was preparing for one last push, out of a war that had consumed many of them for the past six years and left a disoriented nation grasping for its bearings.

Lawrence had a keen sense of history in the making. As the engines of the 60 to 80 armoured fighting vehicles in the yard, known as Strykers, rumbled to life, one by one, he announced: "This is going to put the finishing touches on seven years here. What has been achieved is going to echo throughout the region, prosperity, peace, truth and freedom: the works."

His inner court stood silently. They had just finished a pre-departure rundown of the risks on the road ahead. There was a 10-man bombmaking team active between their staging point, the giant Camp Adder base on the outskirts of Nasireyah, and Basra in Iraq's deep south. If they made it that far, the 40-mile run to Kuwait would be a doddle.

"Go talk to my soldiers, I've got some fine people here and they've done God's duty," said Lawrence. "On our last tour here, we had 22 killed in action; this time we had 10 wounded and no one killed.

"It has been a huge turnaround and it is a measure of the success of our mission here. This time, much of what we have done is handing out [sweets] to children. The engagement with people has been a real highlight."

This drive south was huge in symbolism for the US military, which claims it will no longer play an interventionist role in Iraq.

"When I came in here, I was a brand new soldier," said Staff Sergeant Eligio Marcelo, standing alongside his Stryker. Asked for a sense of what he had accomplished, Marcelo said: "It's 42 months, it's something I accept. Hopefully I'm going to be spending time with my family. This has taken a toll on my family, that's for sure."

From 1 September, the US military plans to implement "Operation New Dawn", a period when it wants to change the relationship between the US and Iraq from that of master and servant to partnership of civilian, democratic equals.

As the soldiers shut down their Strykers and rolled into their quarters in the sprawling tents of Camp Virginia base, near the American-run Ali al-Salem airfield on the outskirts of Kuwait City, a further 56,000 US forces remained on Iraqi soil. At least 6,000 of them will leave Iraq before 1 September, with rest phased out gradually between 1 September and 31 December 2011.

Yesterday, the 4th Stryker brigade were milling around Camp Virginia, where a heatwave shimmered across a stone-filled courtyard, boasting all manner of homespun trappings – a Starbucks, a Taco Bell and the ubiquitous McDonald's.

It is almost certain that there will be further American combat deaths in Iraq, despite today's announcement. US forces will continue to patrol with Iraqi counterparts in some of the country's most restive areas, including Mosul, Diyyala and Kirkuk.

It took 4th Stryker Brigade three days to make the journey across the border into Kuwait. Their journey marks the end to seven years and five months of war in Iraq. Photograph: Carolyn Cole/Polaris/Eyevine

In some ways, Operation New Dawn runs the risk of becoming a false dawn, especially to an American public that has become conditioned to premature claims (think George Bush's "mission accomplished" speech on the flight deck of a warship in 2003).

Colonel Lawrence wasn't buying that, though. "I think we came here at the right time and for the right reasons," he said. "Saddam was a bad man and he is no longer with us. This country has turned the corner. There are systems in place and institutions and the removal of Saddam was a good thing for the region."

Others at Camp Adder had seemed more circumspect. "He's a barrel-chested true believer," said one officer of Lawrence, who admitted to be going through a process of understanding what the past seven years had meant for him. "We admire his passion, but we don't all think like him."

As the Strykers prepared to roll out, one officer, Captain William Marzullo, stepped forward. A battalion physician and veteran of numerous tours, he will retire in six months.

"I was here when they got Saddam," he said of the night in late 2003 when the deposed former president was hauled from a hole near Tikrit. "It was such a sense of mission. We all had those cards (the deck of cards depicting the most-wanted members of Saddam's regime) and one by one they were counted off.

"I thought Bush had the moral high ground right from the beginning," he said. "There has been a change in the mission now though. We are trying to enhance democracy."

Iraq remains without a functioning government six months after the 7 March elections, the third to be held since Baghdad fell. The US military says it is now the state department's turn to take the lead on trying to form one.

Some of Lawrence's charges found it difficult to spell out what they felt they had achieved in Iraq. Many seemed to take comfort from the fact that they had not been getting shot at nearly as much during the past 12 months as they were in 2005.

"It's a lot calmer now," said Staff Sergeant Mike Poole, who had served in Iraq twice before. "There were not as many bullets flying nor roadside bombs. But what it all meant, that's for others to decide. We noticed a big difference with the Iraqi army. We didn't see them at all back then, but now they are running things."

Down the road from the Strykers' staging yard, Brigadier Mark Corson, the commanding General of the 103rd Expeditionary Sustainment Command, whose job it is to move the remaining military hardware out of Iraq, was philosophical about the war's accomplishments.

"I talk to my people about this all the time," he said. "When we got here, it was definitely to deliver Iraq liberation. The place had some big time challenges. We gave Iraqis an opportunity to vote for an elected government and they rushed to do so in bigger numbers than Americans."

Corson presides over vast but rapidly emptying staging yards, some brimming with trucks either heading home, or to Afghanistan. Acres of moon dust cakes many vacant yards, threatening to over-run the base that was a hub of the 2003 drive into Iraq.

"Nobody is going to convince me that we haven't made a major contribution here," said Corson. "Or that we wasted our time here, or that we have not helped this place in some form. I think 2011 is going to be a great year for the Iraqi economy, for business to spring up and get legs under them."

As the Strykers rolled out of Camp Adder for the last time, they passed a giant monolith that said much, according to the history books, about why they, or the nation state of Iraq, was here in the first place. It was the 4,000-year-old Ziggurat of Ur, a temple built near the birthplace of Abraham, one of the oldest manmade structures in the world; a striking icon of the land reputed as the cradle of civilisation.

The Ziggurat soared over the camp's northern fringe as a timeworn reminder of the tenure of this ancient land. Few US forces ever got to visit it.

"I would have like to have understood the significance of it," said one soldier. "But the security was too difficult to organise. I'm told it is amazing and that Abraham was born there. If this place ever settles down the next generations can visit it. That's it for us though. I know this unit has tried its best. We're done. We're going home."