My high school history teacher had a question that she would use to trip up students. In fact, the main thing she tried to do was to teach the kids to answer this question correctly; dates can be looked up, but this one ability is all you need to really benefit from studying history.
The question is: for [x] war, what were the causes and the pretenses?
I've talked about war before (twice), but let me just reiterate: war is almost always the last option. Unless one force is incomparably more powerful than the other, both will do everything they can to avoid it.
Unfortunately, wars do still break out with more frequency than we would like. And when they do, the leaders will justify the action to their people, their peers, and themselves. Noble concepts like freedom and democracy will be invoked. But off the top of my head, I can't really name an instance of the successful seeding of democracy by Big Brother's guns.
I see no way of eliminating wars, but we can do our best to avoid them. For that, we must understand why they happen. Remember this: wars do not happen because of their pretense.
The Iraq war has nothing to do with weapons of mass destruction (which don't exist) or liberating the people (who haven't seen much improvement). The Chechnya wars had nothing to do with independence. The Middle East conflict has absolutely nothing to do with religion. Human conflict is too primal a matter to come about as the result of philosophical discrepancies.
The practical upshot is that once we find the actual causes of wars, we can dispel the myths that prevent us from solving issues most efficiently. I support Israel and its right to defend itself with force, but I do not believe that the billion muslims in the world occupy themselves with plans to murder the other five billion. I support Europe and its way of life, but I do not believe that in twenty years we will all be speaking Chinese. I dislike black pop culture, but I do not believe blacks to be an inferior race.
Human actions are nearly always driven by fundamental motivators. Life, liberty and the pursuit of happiness, if you will (actually liberty is the odd one out - the general population is perfectly happy to live under a reasonably benevolent dictator). This post was inspired by a forum discussion of muslim immigrants being a threat to Europe - and the concern is justified, but here's the problem: a third-generation Moroccan kid, born, raised and educated in Rotterdam, speaking not a word of Arabic, will be a European first and a muslim a distant second.