IMHO we're in Afghanistan because we abandoned the Afghans completely when the Soviet Union pulled out, leaving a power vacuum for the Taliban to fill. What was depicted in "Wilson's War" ( I think that was the name of the movie) is probably true. When the Unites States trained and armed the Afghans and they won the war, the Afghans assumed we would help them build a nation and infrastructure to improve their lives. Instead we just washed our hands of the area, because we accomplished "our" goal of defeating the USSR in the area. Our money and support of the Afghans dried up immediately after the war and that left a political, social void that the Taliban jumped into.

Our goal now is to stop the takeover of Afghanistan by the Taliban, improve education, build roads and schools and finish what we should have done for the Afghans years ago. They expected and probably we're promised these things and now we need to do them to discourage the people from accepting extremist Muslim domination, which is a threat to the rest of the middle east and the US.