Timeline: U.S. Involvement in Iraq

A timeline of U.S. military involvement in Iraq since the terrorist attacks of Sept. 11, 2001:

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Dec. 28: Amid the hunt for Osama bin Laden, President Bush, his advisers and Army Gen. Tommy Franks focus on planning for war in Iraq.

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July 8: President Bush promises to "use all the tools at our disposal" to bring down Iraqi President Saddam Hussein.

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March 19-20: The U.S.-led invasion of Iraq to overthrow Saddam begins.

May 1: Bush declares "major combat operations in Iraq have ended."

Summer 2003: Attacks by an Iraqi insurgency grow and U.S.-led coalition's troop casualties mount.

Dec. 13: Saddam is captured.

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April: Photographs emerge of prisoner abuse at Iraq's Abu Ghraib prison, triggering an international outcry.

June 28: The U.S. occupation authority turns formal power over to interim Iraqi government.

Oct. 6: The top U.S. arms inspector in Iraq finds no evidence that Saddam Hussein's government produced weapons of mass destruction after 1991 -- the primary reason the Bush administration had given for going to war.

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Oct. 15: Iraqi constitution is approved.

Dec. 15: Parliamentary elections are held.

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Feb. 23: At least 136 Iraqis are killed in sectarian violence a day after an explosion destroys the dome of a revered Shiite shrine in Samarra.

August: As sectarian violence increases, U.S. commanders send additional troops to Baghdad.

October: The U.S. military says the bid to cleanse Baghdad is failing and needs to be refocused.

Nov. 7: In what is widely viewed as a repudiation of Bush's Iraq policies, Republicans lose control of both House and Senate in elections.

Nov. 8: Rumsfeld resignation announced; Bush nominates former CIA Director Robert Gates as his successor.

Dec. 31: U.S. military deaths since the start of the war reach 3,000.

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Jan. 10: Bush unveils his retooled war strategy, announcing that 21,500 more Americans will be sent to Iraq.

Jan. 31: Sens. John Warner, R-Va., and Carl Levin, D-Mich., agree on a nonbinding resolution opposing Bush's decision to send more troops to Iraq.

Feb. 5: Republicans block a full Senate debate on the resolution.

Jan-Feb: At least six U.S. helicopters crash or are forced down under hostile fire.

Feb. 13: House begins debating Democratic nonbinding resolution disapproving of the president's troop increase, with vote expected by Friday.