AP

A nearly three-year operation by our troops has ended Friday.

The last of the U.S. troops sent to Afghanistan as part of a surge in 2009 have left the country.

President Obama ordered 33,000 additional troops to help prevent the Taliban from regaining a foothold in the country as the floundering Afghan government struggled to take hold, as well as give NATO troops the time to develop Afghan security forces.

Secretary of Defense Leon Panetta said the surge did accomplish its objectives, as it slowed Taliban momentum and diminished the areas under Taliban control. Panetta characterized the recent green-on-blue attacks committed against NATO forces by Afghan Army and police troops as the last gasp of a desperate insurgency.

Other military leaders, however, have openly referred to the attacks as a serious threat to the war campaign. The attacks have called into question the core strategy that relies on NATO troops working shoulder to shoulder with Afghans, training them to take over the security of their own country so the U.S. and its allies can leave at the end of 2014 as planned.

The withdrawal leaves 68,000 American forces in the war zone.