Agriculture radically modified the habitat. In the arid regions of the Levant where crops were first grown, irrigation facilitated cultivation, reaping surplus food. This allowed higher population densities, labor diversification, trading economies, polity, accumulative culture, ideologies, and depersonalized systems of knowledge, including writing.
Ingrained territoriality birthed property regimes. Whereas foragers had no need for forced labor, those who sought wealth did. Morality evolved to succor materialism and rationalize exploitation, including slavery.
The transition from settlements to political city-states took many millennia. Fertile Crescent homesteads of foragers and craft workers date to at least 12 TYA. The earliest evidence of state authority is 8 thousand years later. In Europe, most peoples were not imposed upon by states until the end of the 15th century.
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Warfare is ultimately not a denial of the human capacity for social cooperation, but merely the most destructive expression of it. ~ English anthropologist Lawrence Keeley
War drove human social evolution. Societies evolved from small tribes which integrated by face-to-face cooperation; their cohesiveness reinforced by the need to further consolidate and defend local resources.
Settlements initially arose on the most fertile lands. Even early on, driven by the social psychology that possession inherently indicated utility, these areas were coveted by others.
As humans settled down, then war becomes more dominant and present. ~ Finnish sociologist Patrik Söderberg
Aggressive competition among tribes grew in scale. This ushered enhanced social specialization and political organization, whereby society layered into a hierarchy.
The minority marshaling the forces of defense and aggression were in position to enforce the invariable inequalities that arose. Ambition and greed are the two sides of the same coin, as economics and politics still demonstrate. Civilization was founded (and still runs) upon the principle that might makes right.
Plutocracies invariably arose in all early civilizations. Socially, obdurate socioeconomic stratification defined early civilization as much as it does in the post-industrial world today. Some things never change.