The fallacy is assuming the nature of civilizations has changed or will continue to get better over time. Human nature is fundamentally warlike, with the subjugation of those tribes deemed lesser, or just in the way of some natural resource. While there is cooperation within individuals in the tribe, history has shown that tribes will conquer rather than cooperate with other tribes given the chance.

This is just the present manifestation of human nature. I assume, just as genocides and war has occurred in the past, they will continue to occur in the present and future, and we will never achieve world peace until human nature itself is changed, perhaps through some future genetic engineering that would make everyone exceedingly docile.