An Oxford in America debate pointed out that Godless Communism killed as many if not more people in the twentieth century than religion did. The debate came out on the side that religion was the main cause. I think it's one cause but anthropologically speaking, from the latest I've read, seen, heard, war and make up were two of our earliest inventions. Both still with us. And probably will. It amuses me when people say we're social animals that thrive with cooperation. Put two people together, for instance, in a marriage, and you get fights. Love and fights. Add another person and the chance of fights increase, disproving the idea that having a child makes a marriage more cohesive. More basically, this particular universe seems to be based on antithesis, duality. As Wallace Stevens put it (roughly), "It was in autumn when the leave were gone, and the limbs bare, I realized eccentricity is the basis of design."

As the human is currently wired war is inevitable. Religion, natural resources and territorial disputes will continue to cause friction well into the future. Gene therapy may help to reduce aggressiveness and religion will gradually loose it hold on the US as it has in Europe. As science successfully opens the door to the universe secularism will be the natural religion.