Mesopotamia at this time was composed of many small, competitive, and vulnerable cities. Mesopotamia’s lack of natural boundaries made it difficult to defend. Egypt, on the other hand, was easily defensible because its territory surrounded one large river (the Nile), with limited access from other places. Its geographic advantages also made Egypt more unified. There was only one language and one pharaoh who ruled the whole Nile River by controlling the boats and the commerce.
However, in the Mesopotamian area, there are two rivers, the Tigris and the Euphrates. There is an upper and lower area, with different altitudes, climates, cultures, and languages. There were nomadic people, who could travel in and out of the desert. There were people that came down from the hills from what is now Iran. There were waves of immigrants, tired of being hunters up in the mountains, coming down into the lush, fertile land. Thus, there were many competing cultures.
When the ancestors of Ether left and moved to the Valley of Nimrod, they were temporarily reversing the usual process. They reverted from an agricultural culture to one of hunter-gatherers. They even named the valley after Nimrod, the great hunter.