Several months ago, The Real News Network had an interview with David Swanson, the author of "War is a Lie", that covered this subject well, I think. Here are the links to the 3 part interview, if you want to see it (the first is more autobiographical, if I remember correctly, but the others are well worth it):
http://www.youtube.com/watch?v=CzwaSbWD8C0http://www.youtube.com/watch?v=BM5qIvVLGg0http://www.youtube.com/watch?v=LIcOdilpXUU
War is cannot be avoided. There will always be war no matter what the date is. It is imbedeed in our genes. War destroy things war also force us to create new things. There are no government that will last forever it will be destroyed by others or it destroys itself. This is just human nature. Humans are predator.
maybe in another 500/5,000/10,000 years, if we're still here,
greed will be left behind and
share will prevail
Why would it? There is no evolutionary pressure to select for "sharing genes". That being said, I don't think greed is the issue. There are plenty of ways to acquire wealth without resorting to war.
No, the real problem with human nature is the tendency of individuals to surrender their individual will to a crowd/mob mentality. That's what allows individuals with malevolent intent to seize power and bewitch the populace, and then go on to do violence. The reason monsters like Hitler or Stalin came to power is not greed, but because others were willing to follow them, were willing to die for them in fact. It is the human ability to
cooperate with each other, to put one's own thoughts and ideas and self-interest and the evidence of their senses out of mind while obeying someone else, that is the fatal flaw that leads to so much war. Without it, it would only be the occasional individual fighting another when they can't get along, rather than those individuals having millions of willing followers slaughtering millions of others.
I'm not convinced by this idea that "war is just part of human nature, and there is nothing you can do about it". As David Swanson put it in the above interview, there has always been a war somewhere, but at the same time there has always not been a war some many more places - in fact, you often have situations in which what led to war in one place didn't in others, despite very similar circumstances. Further, in many cultures, segments of the population (women for example) have traditionally been kept out of conflict; that being typically reserved for men - as he puts it, if women can not do it, why can't men leave it? So, I tend to agree with his explanation that war is mostly a cultural phenomenon: we consider wars to be acceptable, so we enter them, or incite others to do so for our profit.
In this sense, I only partly agree with Bonam; sure, the "group mind" or "gramophone mind", as George Orwell put it in the preface to the Animal Farm, is a problem, and many succumb to it; but you can't forget that, for example in the two cases you presented (Hitler and Stalin), the population at large actually had a lot to gain from their policies. If you weren't one of those being oppressed, both Germans and Russians were living much better off; at least initially - that's one way they managed to hold on to power so easily. So, I don't think it's necessarily the case that people unquestioningly accept that crowd mentality; but rather that they often believe they profit from war, and use the given justifications that they are better than whomever they are busy oppressing at the moment, or that they are somehow actually helping them - look at the US's foreign policy for a good example here.