- drought; lack of hygeine; Climate Change?
Hydraulic Empire - where Monopoly control of water drives the structure of government. Governments were extremely centralized, with no trace of an independent aristocracy - this is completely different to the decentralized Feudalism which existed in medieval Europe. Though tribal societies had structures that were usually personal in nature, exercised by a patriarch over a tribal group related by various degrees of kinship. With hydraulic hierarchies, an impersonal government as a permanent institution was established. Popular revolution was impossible: a dynasty may die out or be overthrown by force, but the new regime (Regime Change) would differ very little from the old one.