Good point, Kurn, son of Mogh! I would add to it that wars have to paid for, so who writes the checks. Usually, wars are financed by selling bonds to rich people. So why do societies write checks? Because they want to make money (or keep their possessions from being plundered). So I would say that every war, and if not every than the vast vast majority are caused by economic interests.

Of course, that doesn't mean that the cannon fodder won't be given a religious speach to pep them up a bit...