Monarchy

The Sumerians seem to have developed one of the world's first systems of monarchy; the early states they formed needed a new form of government in order to govern larger areas and diverse peoples. The very first states in human history, the states of Sumer, seemed to have been ruled by a type of priest-king [...]; among their duties were leading the military, administering trade, judging disputes, and engaging in the most important religious ceremonies. The priest-king ruled through a series of bureaucrats, many of them priests, that carefully surveyed land, assigned fields, and distributed crops after harvest. This new institution of monarchy required the invention of a new legitimation of authority beyond the tribal justification of chieftainship based on concepts of kinship and responsibility. So the Sumerians seemed to have at first justified the monarch's authority based on some sort of divine selection, but later began to assert that the monarch himself was divine and worthy of worship. This legitimation of monarchical authority would serve all the later peoples who settled or imitated Mesopotamian city-states; the only exception were the Hebrews who imitated Mesopotamian kingship but construed the monarchy not as a divine election but as disobedience to Yahweh, the Hebrew god.

http://www.wsu.edu/~dee//MESO/SUMER.HTM