(CNN)Here's a look at the Iraq War which was known as Operation Iraqi Freedom until September 2010, when it was renamed Operation New Dawn. In December 2011, the last US troops in Iraq crossed the border into Kuwait, marking the end of the almost-nine year war.
Timeline
October 16, 2002 - US President George W. Bush signs a congressional resolution authorizing him to go to war to disarm Iraq if Iraqi President Saddam Hussein refuses to give up weapons of mass destruction in compliance with United Nations Security Council resolutions.
November 8, 2002 - The UN Security Council adopts Resolution 1441, giving Iraq a final chance to comply with its "disarmament obligations" and outlining strict new weapons inspections with the goal of completing the disarmament process. The resolution threatens "serious consequences" as a result of Iraq's "continued violations of its obligations."
February 5, 2003 - US Secretary of State Colin Powell makes the case to the UN that Hussein poses an imminent threat.
February 14, 2003 - UN Chief Weapons Inspector Hans Blix reports to the UN Security Council that his team has found no weapons of mass destruction in Iraq.
March 17, 2003 - Bush issues an ultimatum to Hussein and his family - leave Iraq within 48 hours or face military action.
March 19, 2003 - Bush announces US and coalition forces have begun military action against Iraq.
March 20, 2003 - Hussein speaks on Iraqi TV, calling the coalition's attacks "shameful crimes against Iraq and humanity."
March 23, 2003 - Pfc. Jessica Lynch and other members of the 507th Maintenance Company are ambushed and captured outside Nasiriyah, Iraq.
April 9, 2003 - Coalition forces take Baghdad. A large statue of Hussein is toppled in Firdos Square. The White House declares "the regime is gone."
April 13, 2003 - Seven US prisoners of war are rescued by US troops.
May 1, 2003 - Speaking on the USS Abraham Lincoln, Bush declares "major combat operations" over, although some fighting continues.
May 22, 2003 - The UN Security Council approves a resolution acknowledging the US and Great Britain's right to occupy Iraq.
July 22, 2003 - Hussein's sons, Uday and Qusay, are killed by US forces.
December 13, 2003 - Hussein is captured in a "spider hole" in Tikrit. This is not confirmed until December 14 by the US Defense Department.
June 28, 2004 - The handover of sovereignty to the interim Iraqi government takes place two days before the June 30 deadline previously announced by the US-led coalition.
June 30, 2004 - The coalition turns over legal control of Hussein and 11 other former top Iraqi officials to the interim Iraqi government. The United States retains physical custody of the men.
July 1, 2004 - Hussein makes his first appearance in court. He is charged with a variety of crimes, including the invasion of Kuwait and the gassing of the Kurds.
September 6, 2004 - The number of US troops killed in Iraq reaches 1,000.
November 2004 - US and Iraqi forces battle insurgents in Falluja. About 2,000 insurgents are killed. On November 14, Falluja is declared to be liberated.
October 25, 2005 - The number of US troops killed in Iraq reaches 2,000.
November 19, 2005 - At least 24 Iraqi civilians, including women and children, are killed in Haditha. Eight US Marines faced charges in the deaths, but only one was convicted of a crime, that of negligent dereliction of duty.
November 5, 2006 - The Iraqi High Tribunal reaches a verdict in the 1982 Dujail massacre case. Hussein is found guilty and sentenced to death by hanging, pending appeal.
December 30, 2006 - Hussein is hanged.
December 30, 2006 - The number of US troops killed in Iraq reaches 3,000.
January 10, 2007 - A troop surge begins, eventually increasing US troop levels to more than 150,000.
September 3, 2007 - Basra is turned over to local authorities after British troops withdraw from their last military base in Iraq to an airport outside the city.
March 22, 2008 - The number of US troops killed in Iraq reaches 4,000.
July 10, 2008 - Gen. David Petraeus is confirmed by the Senate as commander of US Central Command.
July 16, 2008 - The surge officially ends, and troop levels are reduced.
December 4, 2008 - The Iraqi Presidential Council approves a security agreement that paves the way for the United States to withdraw completely from Iraq by 2011.
January 1, 2009 - The US military hands over control of Baghdad's Green Zone to Iraqi authorities.
February 27, 2009 - US President Barack Obama announces a date for the end of US combat operations in Iraq: August 31, 2010.
June 30, 2009 - US troops pull back from Iraqi cities and towns and Iraqi troops take over the responsibility for security operations. However, US troops remain in the country to continue combat operations and patrols in rural areas.
August 19, 2010 - The last US combat brigade leaves Iraq. A total of 52,000 US troops remain in the country.
September 1, 2010 - Operation Iraqi Freedom is renamed Operation New Dawn to reflect the reduced role US troops will play in securing the country.
May 22, 2011 - The last British military forces in Iraq, 81 Royal Navy sailors patrolling in the Persian Gulf, withdraw from the country. A total of 179 British troops died during the country's eight-year mission in Iraq.
October 17, 2011 - A senior US military official tells CNN that the United States and Iraq have been unable to come to an agreement regarding legal immunity for US troops who would remain in Iraq after the end of the year, effectively ending discussion of maintaining an American force presence after the end of 2011.
October 21, 2011 - Obama announces that virtually all US troops will come home from Iraq by the end of the year. According to a US official, about 150 of the 39,000 troops currently in Iraq will remain to assist in arms sales. The rest will be out of Iraq by December 31.
December 15, 2011 - American troops lower the flag of command that flies over Baghdad, officially ending the US military mission in Iraq.
December 18, 2011 - The last US troops in Iraq cross the border into Kuwait.