War is part of Human Nature. posted by Richard Seymour

[T]he global archaeological record contradicts the idea that war was always a feature of human existence; instead, the record shows that warfare is largely a development of the past 10,000 years.

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[H]ow did peaceful tribal peoples of the distant past turn into the war-prone societies observed in recent centuries? Specific causes are elusive, but I see five preconditions that, in varying combinations, contributed to the onset of warfare in prehistoric times. One was a shift from a nomadic existence to a sedentary one, commonly though not necessarily tied to agriculture. With a vested interest in their lands, food stores, or especially rich fishing sites, people no longer could walk away from trouble.

Another precondition was a growing regional population and probably, in consequence, more competition for resources. Third was the development of social hierarchy, an elite, perhaps with its own interests and rivalries. Fourth was an increasing long-distance trade, particularly in prestige goods: something else worth fighting over. Finally, the first appearance or later intensification of war was often associated with a severe climatic change that broke down the subsistence base.

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My view is that in most cases—not every single one—the decision to wage war involves the pursuit of practical self-interest by those who actually make the decision. The struggle can be joined over basic subsistence resources, but it can just as easily erupt over goods available only to elites. The decision involves weighing the costs of war against other potential hazards to life and well-being. And most definitely, it depends on one’s position in the internal political hierarchy: from New Guinean “big men” to kings and presidents, leaders often favor war because war favors leaders.
Of course, those who push toward war do not make their case in terms of their own selfish interests. Around Amazonian campfires and within modern councils of state, their arguments invoke collective dangers and benefits. But even more, those advocating war always define it in terms of the highest applicable values, whether that involves the need to retaliate against witchcraft, defend the one true religion, or promote democracy. That is the way to sway the undecided and build emotional commitment. And always, it is the other side that somehow brought war on.