In Mesopotamia's small city states, priests ("Ensi"), who had knowledge of writing and the calendar, formed the earliest known formal ruling class. They were stewards or servants of the gods, acting in behalf of the community. 

As conflict with rival city states grew, the priestly rulers came to rely more and more on military leaders who led the city's army and protected the city from outside threats. Over time, the Ensi found their authority challenged by this new class of military leaders, called "Lugal" or King.

As population grew and competition became increasingly severe, military crisis became almost a permanent condition of the area. 

Military rule, by the kind of figure pictured at right - Sargon I of Akkad, a mercenary soldier and the world's first empire-builder – eventually replaced the priestly elite. Warfare was becoming endemic in civilized life.