Why America Failed in Afghanistan

Winning in Afghanistan was always going to be difficult, but avoidable errors have made it impossible.

The United States failed in Afghanistan largely because of intractable grievances, Pakistan’s meddling, and an intense Afghan commitment to resisting occupiers, and it stayed largely because of unrelenting terrorist threats and their effect on U.S. electoral politics. There were few chances to prevail and few chances to get out. 

In this situation, a better outcome demanded an especially well-managed strategy. Perhaps the most important lesson is the value of forethought: considering a variety of outcomes rather than focusing on the preferred one. U.S. presidents and generals repeatedly saw their plans fall short when what they expected to happen did not.

— Read on http://www.foreignaffairs.com/articles/afghanistan/2020-02-10/how-good-war-went-bad