Grass is condensed bio-energy and the ability to utilize this energy imparts great power. Cattle need four stomachs to digest the tough grasses, but humans learned how to harness the seeds, and there was enough food to support a large urban population and civilization was born. Greece, which controlled trade on the calm Mediterranean Sea, would be added later, but it was originally a satellite state of both Egypt and Sumer. Other civilizations would come, but they would be unable to keep up with these first five. All five co-evolved together, but most of the friction was around the proximity of Egypt and Sumer.
Human history follows a path of competition and warfare.
It seems to be dominated by the latest killing technique. First came bronze weapons, then came the chariot, iron and steel weapons, the phalanx, ships, cavalry, guns, the citizen soldiers, airplanes, and most recently, the nuclear bomb. Humans can be a barbaric species with a great potential for violence. While this violence was valuable for their survival on the Savanna, it has become detrimental. The final conquerors were the modern European nation-states, who used science and technology to conquer the world, bringing it together for the first time.