Around 10,000 years ago, during the Neolithic Age, humans began to cultivate plants and to domesticate animals in various parts of the world. Climate change is probably the major reason for the switch from food gathering to food production.
Although farming is often harder than hunting and gathering, agriculturalists, because of their capacity to increase their population, expanded across much of the planet at the expense of hunter-gatherers. The process was gradual and largely peaceful. In some places pastoralism, the dependence on herd animals prevailed.
Megaliths and other monumental structures are products of the diverse religious beliefs and practices of Neolithic societies.
In some places small agricultural villages developed into towns that were centers of trade and home to craftsmen and other specialized professions. Jericho and Çatal Hüyük are two excavated sites that give us vivid glimpses of early Neolithic towns.
Mesopotamia was home to a complex civilization that developed in the plain of the Tigris and Euphrates Rivers beginning in the fourth millennium B.C.E. The elements of civilization initially created by the Sumerians, the earliest known people to live in Mesopotamia, were later taken over and adapted by the Semitic peoples who became dominant in the region. The temples of the gods, the earliest centers of political and economic power, gradually became subordinate to kings. City-states, centered on cities that coalesced out of villages and controlled rural territory, were initially independent but later were united under various empires. Mesopotamian society was divided into three classes: free landowners and professionals in the cities, dependent peasants and artisans on rural estates, and slaves in domestic service. Mesopotamians feared their gods, who embodied the often-violent forces of nature. Cuneiform writing, which originally evolved from a