The U.S. and its allies invaded that country just a few weeks after the Sept. 11 attacks.
Since the invasion, Taliban leaders have been forced out of power and Osama bin Laden was killed.
But after millions of dollars spent, the country is still dealing with insurgent violence.
More than 2,700 U.S. and coalition troops have died in the war in the past decade.
The U.S. still has about 98,000 troops in Afghanistan, but about 33,000 are scheduled to leave by next summer.
On Thursday, hundreds of people marched peacefully through the streets of the Afghan capital, Kabul, demanding the immediate withdrawal of international military forces.
The Associated Press contributed to this report.