Yes Jeffrey, a very valid reason. To get UBL and AQ. Payback for 9-11. We did fight a very smart war in the beginning by helping the 13 tribe Northern Alliance defeat the Taliban. With just a few SF and paramilitary on the ground, letting the Northern Alliance do the ground fighting along with our air power we were able to drive UBL and AQ into the mountains along the Pakistani border. But we failed to capture UBL. We didn't trust the Northern Alliance to go after him, so we began to send in the troops, troops that went into those mountains to hunt UBL and AQ operatives down. More troops begat more troops. Then the original failure of this thing called nation building. Which in my opinion should have never happened.
What the members of the 13 tribe Northern Alliance wanted was to go back to their homelands, their little portion of Afghanistan to be ruled over by their tribal elders and religious leaders. But we knew better, we decided they'd have democracy when they didn't want democracy as their form of government. After all, that was the main reason for fighting the Taliban, The Taliban wanted one man, one tribe to rule over all the tribes. The form of democracy we forced on them, was in essence of one man, one tribe ruling over all the tribes. This caused some of the 13 tribes, once our staunch allies to desert us, to become our enemies, to go over to the Taliban.
If we had let the Afghans, particular the 13 tribe Northern Alliance choose their own form of government, go home to their own area of Afghanistan, we'd have been far better off. We could have left 4-5 SF and or paramilitary folks with each tribe for when the Taliban returned. Once again the Afghans could do the ground fighting, we could call in air support via the SF and paramilitary left with them. This would have been a ongoing thing, but in my opinion, much better than nation building and forcing a form of government on a people that wanted nothing to do with democracy.
It's all history now. We're one arrogant nation. We have no respect for long held traditions and customs of other countries, especially those of Asia and Africa. Although Afghanistan is/was a country on the map. It was never a country in the normal sense of what we realize a country to be. It was a country of 18 tribes, each ruling their own little portion of Afghanistan with shifting alliances depending on the danger to the tribe or tribes from other tribes. To include the USSR and now the USA. We tried to make a country where none really had existed before, not in our sense of what a country is. Then we forced a form of government on them, they didn't want. Will we ever learn?