Well, the reasons for war have always been around, and will continue to be around for the foreseeable future. --Differences in Wealth between people(s). A poor nation wants to invade a rich nation, or take it's technology, or simply expand it's own power base to threaten other countries, or to ward off potential enemies. Whenever there is a riot, the rioters usually go after business or wealthy people in part because of the disparity, but of course greed. The concept of property is an entirely human invention, and unfortunately it does cause division. Even if resources are evenly distributed and shared, eventually when a shortage, either from drainage, or an overpopulation will be certain. Currently the most feared resource is nuclear energy, but in the future, you'd be surprised as we fight over the growing scarcity of clean water. --Resources that we clamor and fight over, such as land, water, food, oil. The rarer, the more greedily we try to take it. An ally today can suddenly become an enemy because they discovered oil, and wouldn't allow you to prospect. Now you have invaded and taken their land by force. --Ideologies can lead to war. Mostly forced ideologies are the cause. As one group will try to control another. Ideologies follow belief in how the world should be, some justified, others not. Everything operates on a certain logic, the logic can be sensible or flawed. But ultimately, if it's an attractive enough change people will fight for that ideology. Or fight to preserve an existing one. --Religion, same as Ideologies. Except, with religion, the way you worship changes over time, and with that new problems emerge. One doesn't need a reason, so long as it's preached to do so. When it comes down to it, religion is a mix of control and racial ignorance. --Racial ignorance. Ignorance plus social race hierarchy are a known poison to society. Genocide has been a long thing in human history. Even the bible shows Jews both committing and suffering genocide in it's long origins. The war against the philistines was a genocide, much like the enemies against their realities in ancient babylonia wanted to ethnically cleanse the strange tribe who worshipped an invisible god. Unless the above are removed, or lessened to a universally acceptable level there will always be some conflict. However, with enough effort. War can be eliminated, at least on paper.