Well, it is a NATO operation right now. Hell, NATO immediately invoked Article 5 right after Sept 11, 2001, which is an attack on one is an attack on all. THe operation is now under NATO command, so yes, it is NATOs battle to win or lose.
Also, Afghanistan was a place were the U.S. could finally hit back at the Communists for Vietnam and kill some Russian boys in large amounts. And we did, big time. Logistics, weapons, mortors, training, medical car, even fucking Tennesse mules were shipped over to carry all of it.The Egyptions, ISraelis, Chinese and British and Pakastanis were all in on this. And to defeat the dreaded Hind attack helicopter, the U.S. finally let the Afghans use the Stinger missile, which took out 7 /10 Hinds that it shot at.
And yes, this was the beginning of the end of the USSR, it was bankrupt and falling to pieces and this battle quickened its demise.
And lets not forget, before the US began throwing 1.2 billion dollars (600 mil from us and 600 mil from Saudi Arabia) The muji's were in dire trouble, the Soviets were not fighting to gain terroritory from them as much as it was an all out genocide. Without our help, they would have fallen. The country would be in a constant state of war, it always has been, but the Russians could have gotten the oil and scared the shit out of the larger M.E.
A great book to read on this was "Chralie Wilsons War" by George Crile. I had to read it for a foreign policy class a while ago and it is a wild book. Def. recommend it.