In the beginning, it all looked simple: topple Saddam Hussein, destroy his purported weapons of mass destruction and lay the foundation for a pro-Western government in the heart of the Arab world.
Nearly 4,500 American and more than 100,000 Iraqi lives later, the objective became simply to get out - and leave behind a country where democracy has at least a chance, where Iran does not dominate and where conditions may not be good but "good enough."
Even those modest goals may prove too ambitious after American forces leave and Iraq begins to chart its own course. How the Iraqis fare in the coming years will determine how history judges a war which became among the most politically contentious in American history.
Toppling Saddam was the easy part. Television images from the days following the March 20, 2003, start of the war made the conflict look relatively painless, like a certain type of Hollywood movie: American tanks speeding across the bleak and featureless Iraqi plains, huge blasts rattling Baghdad in the "shock and awe" bombing and the statue of the dictator tumbling down from his pedestal.
But Americans soon collided with the complex realities of an alien society few of them knew or understood. Who were the real power brokers? This ayatollah or that Sunni chief? What were the right buttons to push? America had its own ideas of the new Iraq. Did most Iraqis share them?
Image: US President Barack Obama salutes as Vice President Joe Biden, Deputy Defense Secretary Ashton Carter and Chairman of the Joint Chiefs of Staff General Martin Dempsey look on during a ceremony to mark the return of the US Forces - Iraq colors December 20, 2011 at Andrews Air Force Base in Maryland. The event marks the end of the Iraq war after the last US combat troops rolled out of Iraq into Kuwait on December 18.