That argument about war being 'human nature' is totally bull shit. Conflict among small groups of people may be inevitable; if you stole my moped I'd probably want to hit you in the face.
War on the other hand is when the elite of a nation-state coerce the people who just so happen to live within its borders (through a draft, patriotism, fear, poverty, whatever) to go to another country and kill people.
How often do the people that actually end up fighting the war have something to gain from it? It's NOT 'human nature,' unless you're some kind of Ayn Rand or some bull shit, and even Greenspan admitted that shit was way off.