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.

U.S. President George W. Bush listens as U.S. Army soldiers sing quotThe Army Songquot during a stop at Fort Hood, Texas, January 3, 2003. Bush addressed the soldiers and their families about the possiblity of military action against Iraq.
U.S. President George W. Bush listens as U.S. Army soldiers sing "The Army Song" during a stop at Fort Hood, Texas, January 3, 2003. Bush addressed the soldiers and their families about the possiblity of military action against Iraq. Reuters
Smoke rises from an unidentified building as explosions rocks Baghdad during air strikes March 21, 2003. U.S.-led forces unleashed a devastating blitz on Baghdad on Friday night, triggering giant fireballs and deafening explosions and sending huge mushroo
Smoke rises from an unidentified building as explosions rocks Baghdad during air strikes March 21, 2003. U.S.-led forces unleashed a devastating blitz on Baghdad on Friday night, triggering giant fireballs and deafening explosions and sending huge mushroom clouds above the city centre. Missiles slammed into the main palace complex of President Saddam Hussein on the bank of the Tigris River, and key government buildings, in an on slaught that far exceeded strikes that launched the war Reuters
Iraq Ethnic Conflict
Iraq – Ethnic Conflict. The current American occupation of Iraq, which has lasted eight years, has resulted in at least 100,000 civilian causalities. Local insurgents, terrorism, explosive devices, mines, suicide bombers, car bombs and gunmen are very common in Iraq. Reuters
U.S. Navy Hospital Corpsman HM1 Richard Barnett, assigned to the 1st Marine Division, holds an Iraqi child in central Iraq in this March 29, 2003 file photo. Confused front line crossfire ripped apart an Iraqi family after local soldiers appeared to force
U.S. Navy Hospital Corpsman HM1 Richard Barnett, assigned to the 1st Marine Division, holds an Iraqi child in central Iraq in this March 29, 2003 file photo. Confused front line crossfire ripped apart an Iraqi family after local soldiers appeared to force civilians towards positions held by U.S. Marines. Reuters
An Iraqi man throws stones at a statue of Iraqs President Saddam Hussein as it falls in central Baghdad April 9, 2003. U.S. troops pulled down a 20-foot six metre high statue of President Saddam Hussein in central Baghdad on Wednesday and Iraqis d
An Iraqi man throws stones at a statue of Iraq's President Saddam Hussein as it falls in central Baghdad on April 9, 2003. Iraq is again facing a "serious crisis," Kurdistan's leader Massoud Barzani said during a recent visit in Washington -- and his semiautonomous region's ambitions in the oil-and-gas business aren't going to help defuse potentially explosive ethnic tensions. Reuters
An Iraqi policeman keeps an eye on the crowd as a British military policeman searches a gunman who was shot by coalition soldiers after he threatened a joint police patrol with a rocket launcher in the Hayaniya neighbourhood of Basra May 20, 2003
An Iraqi policeman keeps an eye on the crowd as a British military policeman searches a gunman who was shot by coalition soldiers after he threatened a joint police patrol with a rocket launcher in the Hayaniya neighbourhood of Basra May 20, 2003 Reuters
Terrified Iraqi children protect themselves from the cold after they039re taken outside their house during a pre-dawn raid in a suburb of Baquba November 16, 2003. Looking for members of a suspected terrorist cell who attacked coalition forces, troops
Terrified Iraqi children protect themselves from the cold after they're taken outside their house during a pre-dawn raid in a suburb of Baquba November 16, 2003. [Looking for members of a suspected terrorist cell who attacked coalition forces, troops of the U.S. Army's 4th Infantry Division (Task Force Ironhorse) detained several Iraqi men after shots were fired at an assault team during an early morning operation.] Reuters
White house Barack obama Afghanistan George W. Bush