Sept. 11, 2001 -- Al-Qaeda operatives hijack four commercial airliners, flying two into New York's World Trade Center and a third into the Pentagon. A fourth plane crashes in a field near the town of Shanksville, Pa., after passengers storm the cockpit. Nearly 3,000 people die in the attacks.
Sept. 18, 2001 -- President George W. Bush signs a resolution authorizing the use of force against those behind the 9/11 attacks.
Oct. 7, 2001 --The U.S.-led bombing against Taliban forces begins, followed by ground forces 12 days later.
Dec. 9, 2001 -- The Taliban surrenders Kandahar and Taliban leader Mullah Omar flees the city.
December 2001 -- Afghan militias track Osama bin Laden to the Tora Bora cave complex southeast of Kabul and begin a fierce two-week battle with al-Qaeda militants. Several hundred are killed, but bin Laden escapes.
May 1, 2003 -- Defense Secretary Donald Rumsfeld declares an end to "major combat" in Afghanistan.
August 2003 -- NATO assumes control of security forces in Afghanistan, and the mission of expanding their roll outside Kabul.
April 22, 2004 -- Former NFL star Pat Tillman is killed in a friendly fire incident during a firefight with hostile forces in Sperah, Afghanistan. The Army first reported that Tillman had been killed by enemy fire, and then Lt. Gen. Stanley A. McChrystal approved the award of a Silver Star.
Oct. 9, 2004 -- Karzai becomes the first democratically elected head of Afghanistan, months after an assembly of 502 delegates drafts a constitution.
July 2006 -- Violence surges in Afghanistan, with intense fighting erupting in the south and a rise in suicide attacks and remote-detonated bombs.
Feb. 27, 2007 -- A suicide bomber attacks the entrance to Bagram Air Base during a visit by Vice President Dick Cheney, killing 23 people. The Taliban claims responsibility, saying Cheney was the target, although he was not injured.
Feb. 27, 2008 -- A suicide bomber kills more than 100 people in Kandahar. Officials call it the deadliest suicide bombing of the war.
Feb. 17, 2009 -- Newly-inaugurated President Barack Obama announces 30,000 additional troops will be sent to Afghanistan in a move similar to an earlier troop surge in Iraq.
July 2009 -- The U.S. military launches a major offensive to quell increasing Taliban insurgents in the south.
July 2010 -- A record 66 U.S. troops are killed, making it the deadliest month in the nearly nine-year war. U.S. commanders said more troops were dying because of stiffening Taliban resistance.
July 25, 2010 -- WikiLeaks releases more than 90,000 leaked documents pertaining to the war in Afghanistan. Pfc. Bradley Manning is jailed after being accused of leaking documents to the website.
May 2, 2011 -- President Barack Obama announces that U.S. forces have killed Osama bin Laden during a night raid of a compound in Abbottabad, Pakistan.
Aug. 6, 2011 -- A U.S. Chinook military helicopter (similar to the one pictured) containing members of SEAL Team 6 is shot down in Afghanistan, killing 38, including 22 Navy SEALs. It's the largest single loss of U.S. life since the beginning of the war.
June 22, 2011 -- President Barack Obama announces that 10,000 U.S. troops will be withdrawn from Afghanistan by the end of 2011, and an additional 23,000 will leave by the summer of 2012.
March 2012 -- U.S. Army Staff Sgt. Robert Bales is accused of killing 16 Afghan civilians in an armed rampage in the Panjwai district of Kandahar.
April 2012 -- The Taliban announces a "spring offensive," with an audacious attack on the diplomatic quarter of Kabul. Security forces kill 38 militants.
May 2012 -- At a summit in Lisbon, NATO endorses a plan to withdraw foreign combat troops and hand over security to Afghan forces by the end of 2014.
June 18, 2013 -- NATO-led troops transfer security responsibility to Afghan forces. The United States and an Afghan government group dedicated to peace and reconciliation announce plans to hold talks with the Taliban militant group in Qatar.