History of the world
Whether in prehistoric or historic times, people always needed to be near reliable sources of potable water. Settlements developed on river banks as early as 3000 BCE in Mesopotamia, on the banks of Egypt's Nile River, in the Indus River valley, and along China's rivers. As farming developed, grain agriculture became more sophisticated and prompted a division of labour to store food between growing seasons. Labour divisions led to the rise of a leisured upper class and the development of cities, which provided the foundation for civilization. The growing complexity of human societies necessitated systems of accounting and writing.
State (polity)
Mesopotamia is generally considered to be the location of the earliest civilization or complex society, meaning that it contained cities, full-time division of labor, social concentration of wealth into capital, unequal distribution of wealth, ruling classes, community ties based on residency rather than kinship, long distance trade, monumental architecture, standardized forms of art and culture, writing, and mathematics and science. It was the world's first literate civilization, and formed the first sets of written laws.