Hydraulic Despotism

Food, water, and air- these things are necessary for life. On alien worlds, these necessities can often be far harder to obtain than they are beneath Earth’s kinder skies. A ruler who manages to seize control of one or more of these necessities can hold entire worlds in helpless thrall.
Hydraulic despotisms appear most often on worlds without a breathable atmosphere, or with minimal water supplies, or those lacking in some important trace nutrient. Control of this necessity is ruthlessly restricted by the despot and his minions, and they will go to extraordinary lengths to ensure that no competing source can arise. Once the monopoly is broken, however, these despotisms tend to crumble overnight as the bitter populace takes its vengeance on the tyrant and his servants.
The prime law of any hydraulic despotism is the control of whatever substance the despot uses to rule the populace. Offworlders who bring in alternate supplies are met with brutal suppression, but those who actually bring in alternate means of producing the necessity are a mortal threat to the state’s very survival, and treated accordingly. For commoners, punishments often revolve around restricting access to the necessity, with judges and security personnel rewarded with greater abundance.