As an Infantry soldier, and, having a lot of knowledge on the Vietnam war, I can say we did not LOSE for a lack of motivation, but more for a lack of non-restraint. Politicans are Morons, and most don't know squat about warfare. They love to send soldiers into a combat area, but because of "politics", the love to limit the ability of the soldier but limiting the tools he can use, and limiting what he can do.
We were trained to be effective stone cold killers. Thats that, plain a simple. When you send us to war, we will mess the enemies shiz up, and all we ask, is if your not fighting by our side, you stand in the rear and let us do our job. Its when we are restrained, we are kept from doing what is NEEDED to be done to win.
Two good examples rise of out this from both Vietnam and Somolia.
#1. In Vietnam, we KNEW the Vietcong were using boardering countries (Loas etc) to move equipment. We would not move into these countries in FORCE to stop them before they moved very far south because of "Politics". Soldiers were restrained from doing what needed to be done to finish the job, thus, eventually, we had to leave.
#2. Somolia. When the Task force ranger moved into Mogadishu and got caught in a big firefight, what was needed to get them out was armor. Politicans decided it would not be politically correct to send armor to somolia because it would not be politically correct since it was not a war. But they send in soldiers to fight a war in the city. 18 soldiers died because of this logistical blunder.
So don't say for a second it was the fault of the US fighting men and women who would have been beaten, blame the politicians for their logisitical bluders/F**ked up ideas.
Oh yeah, for any of you who have read black hawk down, check this out.
http://www.nightstalkers.com/tfranger/movie/Default.html
Read this if you want to know what went wrong in somolia.
http://www.specialoperations.com/Operations/Restore_Hope/97-0364.pdf
-Jason