The two main rivers are Tigris River, and Euphrates River.
The plains covered a large area of land, and few people lived there.
Zagros Is the foothill that they moved to.
farmers in the Zagros foothills did not have enough land to grow food for the increasing population. As a result, villages began to suffer from food shortages.
Faced with such dramatic seasonal changes, farmers were constantly struggling to raise crops with either too little or too much water.
Sumerian farmers began creating irrigation systems for their fields. They built levees along the sides of the river to prevent flooding. When the land was dry, the farmers poked holes in the levees, allowing the water to flow through the holes and into the thirsty fields.
As the Sumerians worked together, they began to create larger communities.
Canals became clogged with silt, so farmers had to clean them regularly. One clogged canal could disrupt the entire system.
They fought over the right to use more water.built new canals, or blocked other cities' canals. In this way, they kept water from reaching the cities that were downriver.The plains provided no natural barriers. There were no mountain ranges or rushing rivers to keep out enemies.
To control the water supply, Sumerians built a complex irrigation system. The system crossed village boundaries, so the Sumerians had to cooperate with one another. This led them to live in larger communities—the first city-states.