Do you think someone can come from the other side of the planet and kill your family members two generations ago and still *make* you friendly to them? Probably not.

There are instances where conquered nations have turned friendly - Japan comes to mind, but Japan did not share every mile of their border with nations hostile to the occupying force (us), and who were more than happy to fund and supply an ongoing insurgency.

But Afghanistan IS completely surrounded by nations that really don't like America. It didn't matter how long we stayed - it was never going to work the way you think it should.