As U.S. forces conclude their withdrawal from Iraq this month, nowhere will the change be more evident than in the heavily fortified compound in central Baghdad known as the Green Zone.
Once the secretive and ornate command center of Saddam Hussein's rule, the approximately six-square-kilometer district next to the Tigris River has served as the hub of American military and diplomatic activity in Iraq since the U.S. invasion in 2003.
Formally named the International Zone, the area is ringed by high walls and has heavy security at every entrance. U.S. military officials informally called it the Green Zone to differentiate from what they call the Red Zone - all those areas outside the walls where American soldiers and contractors have been highly vulnerable to attacks.
Even before the U.S. invasion in 2001, parts of the zone were off-limits to the average Iraqi. The complex included several of Saddam's ornate palaces, villas used only by the Iraqi leader and his inner circle, and well-manicured parks. At one time, there was a private zoo on the grounds.
American military analyst John Pike said U.S. forces decided shortly after entering Baghdad that the easily defended zone would make an ideal place to set up central operations.
"It did not require a great deal of thought on the part of the Americans to decide this was the place," Pike said.
Through the years, the complex suffered regular mortar and rockets attacks from Iraqi insurgents. Bombs exploded outside the gates. And because of the threat of violence against vehicle convoys, helicopters ferried top U.S. military and political figures between the zone and Baghdad's airport.
The U.S. formally transferred control of the Green Zone to Iraq in 2009, setting off a gradual reduction in the American presence in Iraq. But thousands of U.S. diplomats and troops remained in the zone.
Their numbers will now be smaller, but some Americans will remain, mainly those working in the U.S. embassy or with a detail of private security contractors.
Reports from Baghdad say getting in and out of the zone has not become any easier since control was transferred to the Iraqi government, which has added its own layers of security.
Some information for this report was provided by AP, AFP and Reuters.