I agree with a lot of the replies that have gone on (great topic, by the way), but the OP, by focussing exclusively on the USA, gives a bit of a skewed reading of why other countries fight wars.
For example, from a US perspective, hatred doesn’t have much place, because of its multicultural and isolated nature (it applies to my country - Australia - as well). When a war “has” to be fought, the enemy has to be actively demonised, whether it’s the Viet-Cong or Saddam Hussein. I’m not saying these enemies were actually good people, just that the vast majority of Americans would have been completely neutral in their assessment of them if it weren’t for the media going over their crimes continually.
On the other hand, in countries where there are ‘natural’ enemies, which go back sometimes a number of centuries, there is no reason to contrive hatred - it’s already a part of the national character (and this is not a racial thing at all - it happens on both sides of any of these conflicts). A good, but tragic, example of this is in Yugoslavia, where historical hatred is so entrenched, war is almost inevitable, even if it’s not ongoing. That’s part of America’s problem when trying to settle these conflicts - they imagine that if they can get the people from each nation together around a table and shake hands, and maybe work out some economic issues, everything will be OK. The reality of national hatred is a sad but ongoing one.
Hatred can also sometimes override the other reasons for war in ways that we can think of as irrational. Hitler, for example, prioritised the murder of Jews over the deployment of troops to strategically important positions, and a number of historians suggest this was one of the factors which led to his defeat. This is an extreme example, but its fundamental elements are not unique.
War is not always ‘rational’, as it would be if it was always about a country wanting to gain land or money.
HenrySpencer.