Where and how did river basins contribute directly to the emergence of cities, from 3500-2000 BCE? What were some similarities and differences in irrigation techniques among these early civilizations?

The river basins contributed to the emergence of civilizations because it stopped the nomadic way of life. People began to settle and farm and this occurred in the Mesopotamian civilization which is in modern day Iraq. They use the Tigris and Euphrates river. Later in the same area emerged the Sumerian civilization.