One step that may be good is clearly defining where a war stops being a retaliation for something in the past and becomes a war of aggression. Whether or not t

One step that may be good is clearly defining where a war stops being a retaliation for something in the past and becomes a war of aggression. Whether or not the current situation in Ukraine is one of aggression depends largely on whether or not you feel that the Western involvement in the Orange and Maidan revolutions were aggressive in the first place, and whether or not the response to their aftermath is warranted. All sides are probably at least a little wrong here, and ultimately, it probably boils down to a feud between Russia and various aspects of the West going at least back to the Crimean war, if not earlier, and the back and forth animosity that has perpetuated the cycle over that time. Perhaps the question then isn't "how can we prevent launching wars of aggression," but rather "how can we successfully reach an agreement where all sides agree to finally bury the hatchet." As long as we refuse to consider the longer cycle of revenge and posturing at play we'll likely continue to be confused in the face of it perpetuating itself.