The stakes in Afghanistan now echo what caused the U.S. to invade almost 11 years ago: the threat of more al-Qaida attacks.
The U.S. and its allies plan to end their combat role in Afghanistan by the close of 2014, leaving the Afghans fully in charge. There's fear, however, that the Afghans won't be capable of self-defense and the Taliban could regain power. That would open the way for al-Qaida to launch attacks on the United States from within the country, as the terrorist group did on Sept. 11, 2001.
More than 2,000 U.S. troops have died in Afghanistan since then.
Al-Qaida leader Osama bin Laden was killed by U.S. forces in Pakistan last year. Al-Qaida remains a threat, however, with its fighters dispersed around various spots in the Middle East and North Africa.