This is really a bit of BS propaganda that seems to have crept into the US military psyche in the post Vietnam era. The US is notorious for leaving people behind and thats why they stick to that mantra. If you tell a lie often enough it becomes truth.

The US has left people behind at just about every war since WW2. In the Phillipines it was as a result of unfortunate circumstances and military neccesity, but in Korea and Vietnam it was out of political expiediency and that is pretty apalling. Somalia folks were left behind again. And it is suspected that it may have again occured at the end of Gulf War 1. The portrayal of "Leave no one behind" only exists because the US has continually done so. I'm not trying to flame even though it looks like that, but the myth in no way reflects the reality.