I honestly don't think it's pessimistic to predict war. We live in a world where various cultures have incompatible values at a fundamental level that include valuing the extinction of other cultures. If they never go to war it means that one or the other side wins and the values of the other side are effectively suppressed. To me the possibility of war is less bad than permanent oppression or extinction. It would mean the end of the evolution of human values that are worth dying for. That version of humanity is nerfed beyond the ability of ability to persist across the changes the future will bring.

War is as evil as death, but death was necessary to our creation, and ending death would cripple human adaptation and doom the species. Without a willingness to fight for our beliefs we would be evolutionary cannon fodder.