The growing opinion in Europe is that Afghanistan is the United States’ "new Vietnam." The truth is that it is worse than Vietnam.
In Vietnam, the United States had a clearly identified enemy, supported by a responsible Communist state in North Vietnam with its government in Hanoi. The U.S. had a theory about what it was doing: suppressing the insurrection in the South, and bombing North Vietnam until the government stopped the war. All of this was, in principle, possible.
However the U.S. acted on a nonsensical theory about the world "going Communist" if the U.S. didn’t win, just as today the U.S. has an even more nonsensical theory about radical Islam conquering Muslim Asia and all of Europe, and then attacking the U.S., if Washington fails.
Unlike the Viet Cong, the Taliban are not a disciplined force acting under some government’s orders, and have neither the intention nor means to attack anybody outside Central Asia. They are motivated by nationalism, today focused against the United States, and by a desire to propagate their form of Islam