This document provides an overview of early civilizations that developed along major river valleys, focusing on Mesopotamia. It describes the geography of the Fertile Crescent region and how the unpredictable Tigris and Euphrates rivers led people to develop irrigation, bricks, and trade. City-states emerged, initially led by priests but later also by military leaders. Cultural diffusion increased as Sumerian cities prospered. Constant warfare weakened city-states, leading to the rise of empires like Akkad and Babylonia under rulers like Sargon and Hammurabi, who developed one of history's first legal codes.