WORLD CIVILIZATION

Detailed explanation-1: -The Sumerian city-states were not united as one entity; instead, they all were their own independent states (Yoffee). This allowed violent conflicts to occur between the city-states because they had no central authority in place to prevent war.

Detailed explanation-2: -So Sumerians began to build strong walls around their cities. The walls were made of mud bricks that were baked in the sun until they were hard. The Sumerians also dug moats outside the city walls to prevent enemies from entering the city. Most people lived in houses behind the walls, while the farms lay outside.