One lesson of Vietnam is that war may not be such a bad thing, because it tends to destablize the ruling class in a long run. During the long period of reliative peace that followed, and the collapse of the USSR that reduced the threat of war even further, the fat cats grew stronger and and stronger. So if the next war is a long one, a lot of USers come home in body bags, and the fanatics bring the war to the US soil as they did on 9/11 - that may destablize the ruiling class once again.
Wojtek