President Barack Obama announced the withdrawal of U.S. troops (by the end of 2011), in the briefing room of the White House, on Oct. 21. He further said that the United States would fulfill its promise of pulling troops out of Iraq.

Since former President George W. Bush declared war on Iraq in 2003, more than 4,000 American soldiers have lost their lives. Over that period, the U.S. has spent an estimated $3.2 trillion, to finance wars in Iraq and Afghanistan, according to a study by Brown University.

While Iraq was quickly defeated and Saddam Hussein eventually captured and executed, it has taken, apparently, another 8 years before the Iraqi government and security forces have been considered strong enough for the U.S. to withdraw.

The United States had previously agreed to leave between 3,000 and 5,000 troops in Iraq as trainers. However, following failed negotiations with the Iraqi government, a residual 150 troops will continue to remain in the country. The current military presence in Iraq stands at just under 40,000.

Take a look at some of the defining moments of the nine-year war.