By Paul Wood
BBC News, Baghdad
On a hot, fetid day, just outside Falluja, 2nd Lt Ilario Pantano of the US Marines told me what the Iraq invasion had been for.
Ilario Pantano's case highlights the complexity of the US role in Iraq
"I'm a New Yorker and 9/11 was a pretty significant event for me," he said.
"Our duty as Marines is, quite frankly, to export violence to the four corners of the globe, to make sure that this doesn't happen again."
US forces entered Iraq two years ago, most believing - as many Americans still do - that Saddam Hussein had something to do with the 11 September 2001 attacks.
Lt Pantano left a highly paid job in New York to re-enlist in the Marines after 10 years as a civilian.
So when I met him near Falluja, in June of last year, his life was almost a recruiting ad for the Marines, an example of the idealism surrounding America's Iraq adventure.
Now, he has just become the first US serviceman from Iraq to be charged with murder. He is accused of killing two unarmed Iraqis, shooting them in the back, and putting their bodies on display as a warning to others.
Lt Pantano denies the charges. But the accusations against him, along with the Abu Ghraib prison scandal and the growing insurgency, all show how Iraq has turned out to be so much more complicated than the Americans ever expected.
Reduced to rubble
So far, more than 1,500 US servicemen and women have died in Iraq - 10 times the number killed in the "major combat operations" that President Bush said had ended on 1 May 2003.
And - literally - countless thousands of Iraqi civilians have lost their lives.
Just after President Bush made his declaration, I met Saed Abbas, whose wife and six children all died in an American airstrike.
Despite the dangers, Iraqi elections went ahead in January
In fact, 43 members of his extended family were killed by the single missile. His brother lost his six children; his sister, seven.
They had left Baghdad when the invasion started, thinking the countryside would be safer. They crammed into a single farm house, sleeping head-to-toe on the floor.
The entire building was reduced to fist-sized pieces of rubble. "I was shouting for my family, but no-one replied," Saed said, slowly turning over photographs of his children, "I could hear only screaming."
Despite his almost unimaginable tragedy, Mr Abbas was not angry at President Bush and he did not support armed "resistance".
He was one of those ordinary Iraqis for whom the coalition says the war was fought.
Image of hope
Millions of those ordinary Iraqis joyously cast their ballots for the first time in the elections in January.
This was one of the most hopeful images of the past two years. It seemed, finally, to fulfil the promise of the single moment which came to define the invasion - when the huge bronze statue of Saddam Hussein came crashing from its plinth amid the roar of the crowd in April 2003.
Was this the start of blooming Middle East democracy?
The White House hopes democracy will now bloom all over the Middle East.
Weapons of mass destruction were not found; Saddam Hussein's conventional arms are still being used to kill American soldiers; the CIA admits al-Qaeda has gained many new recruits because of the occupation.
The invasion itself was a remarkable victory, a swift and crushing blow against an exhausted country. Still, the overall Iraq "balance sheet" remains difficult to read.
A measure of the post-invasion success will be when the coalition is able to leave. And two years on, for the 150,000 American troops in Iraq, there is still no end in sight.