WARNING: GRAPHIC CONTENT Ten years ago, U.S. forces began bombing Afghanistan in retaliation against its Taliban rulers who refused to hand over the al Qaeda leaders responsible for the Sept. 11, 2001 attacks on the United States. Within weeks, the air strikes had helped Afghan opponents topple the Taliban, but in the decade since, the deposed Islamist fighters have returned to mount an ever more aggressive insurgency against an Afghan government backed by the United States and NATO. Since U.S. President Barack Obama took office in 2009, the U.S. force has tripled in size, but Washington and NATO now plan to begin withdrawing and to hand over responsibility for Afghanistan's security to Afghan forces by 2014. 50 PHOTOS