Even the lessons of RVN are now forgotten when discussions take place about asymmetric warfare. The unchallenged assumption is that we were beaten by an unconventional guerilla force because of their determination to throw us out of the country. Untrue. They won that conflict in the newspapers of our own country, in the halls of Congress, and in executive office staff conferences. Our military application of availanle resources was limited by politics not by potential.
As for civilians fighting, a case in point are the Sammis in Mogadishu. Sure we dropped a lot of them but they kept coming.
Yes we left Viet Nam unbeaten but we couldn't destroy the Norths will to fight on. If we had left South Korea after the truce, I'm sure the end would have been the same.
Basically, you don't know how the masses will react to a full-blown invasion of their nation.
We were lucky in Afghanistan. There was a strong, well-equipted opposition force waiting to help out when we arrived.