Grain surplus, beer and social differentiation.
The situation changes around 4700 BC in Mesopotamia. Villages and their cultivated areas are agglomerated into urban centres established along the waterways. The controlled territories cover on average 100 km2 and include the upstream villages. These rudimentary regional organisations include hamlets, settlements, villages and first urban centres. They are based on economic cooperation and the emergence of a politico-religious hierarchy.
Urban entities such as Ur, Eridu and Uqair are characterised by their political stability, their irrigated agriculture generating important grain surpluses, an economic specialisation among the population, a regional and not only local political centralisation, and finally a more or less planned economic organisation (vast buildings associated with grain reserves, collective granaries and large storage jars, collective irrigation works).
The accumulation of prestige products is low (weapons, precious metals, rare materials, jewellery, etc.). The latter are usually a sign of social inequality based on the barter of rare products, war or strategies of expansion by force, those ordered by a minority for its own benefit.
How to interpret these data and understand the dynamics of recent (5300-4000) obeidian culture? How do we move from small, relatively autarkic agrarian communities to hierarchical regional societies? What role did the beer brewing play in this evolution?
The researchers propose two models for understanding the success of the first centres of expanded power, which will be called " chiefdoms " for the sake of convenience.
 A. Johnson, T.K. Earle, 1987 : The Evolution of Human Society: from Forager Group to Agrarian State, 208, 222.