Why sumerians were different from other people of their time?

The peoples of Sumer are among the earliest denizens of Mesopotamia. By about 4000 BCE, the Sumerians had organized themselves into several city-states that were spread throughout the southern part of the region. These city-states were independent of one another and were fully self-reliant centers, each surrounding a temple that was dedicated to god or goddess specific to that city-state. Each city-state was governed by a priest king.