The cities in Vampire: The Requiem operate in a neo-feudal organization. Like feudalism in Europe from the 10th to the 14th centuries, power is decentralized based on fiefdoms with the local lord holding more sway over his people than the king. The lord then divides up his land to knights that swear allegiance to him. On rare occasions, these knights might divide up their land further.
But in neo-feudalism, fiefdoms are limited to metropolitan areas. Because each area is surrounded by werewolves and traveling during the day is dangerous, each city is isolated from the other. Thus there is no king. Power stops at the local lord, called the Prince. The Prince's domain can be divided up amongst those he choose, but it is less common than lords divvying up amongst knights. The exception is particularly large domain, where more levels of power is the only way to keep the city in order.
Also, not all cities are ruled the same. While most resemble a feudal monarchy, some resemble a corporate boardroom with a group of elders making most of the decisions (though there is still a prince). A more religious take is the diocese, which operates much like a theocratic monarchy. The Lancea Sanctum often form these governments when they are in power.