* Theres a book called The Running Man that explains this in more detail.* The americans came back from the war and started hating the Vietnamese - they called it the Vietnam War, whereas the Vietnamese call it the American War. Also, there was a stereotypical depiction of a Vietnam War Veteran as a mad, reclusive person who is dangerous to be around (due to all the horrific things e.g. Traps with kids pretending that their mother is dying and then a bomb killing them when they follow the kid). American Society has changed from being a friendly walk in the dark alleyway place (still portrayed as this in movies) where communities come together i.e. Decorate all their houses for christmas. Instead of this welcoming, friendly attitude towards neighbours, more and more people are becoming like the older (30-40s) generation of the English and Australians. (Not to say that this is a bad thing).
Many young American solders died in the war , making the American Society population less.