How did geography impact the Tigris/Euphrates civilization?

The civilization of the Tigris and Euphrates river valleys has had very big benefit from the geography of the area. All of the area is arid and dominated with desert around these two rivers, which has been a natural protector of this civilization, as most of the people were not willing to risk it to go through the desert. In the middle of the desert though, the two rivers were changing the landscape, providing water for drinking and irrigation, as well as fertile layers of soil, making it an excellent place for agriculture. Since the agriculture was able to flourish, this civilization was producing a surplus of food, using it fro trade, while the spare time was committed to learning, science, philosophy.