Preventing Modern wars
Clinical psychology has evolved effective techniques for dealing with anger, and these techniques can be translated to international politics.
Essentially, we help a person with anger issues to recognise the first beginnings of the feelings or situations that will escalate to an outburst of anger, and we teach them ways of diverting away from the path that leads to anger.
The United Nations can use this same approach to war, looking out for disagreements and tendencies and using negotiation in the early stages of problem formation, rather than letting things slide into military action.
These links will lead to a page on how each main causal factor may be addressed:
Addenda
A More Peaceful World 