How does the U S constitution republic compare to authoritarian forms of government?

In a constitutional republic like the US, the head of state and other representatives are chosen by the population. There is also a constitution, which limits the power of the members of the government, and guarantees separation of powers - Legislative (the making of the laws), Executive (the realization of these laws), and Judicial Branch (which decides if these laws have been broken).

On the other hand, authoritarian forms of government are:

Absolute monarchy: The ruler has absolute power. There are no laws to limit the ruler's power. Constitutional monarchy: The monarch exercises power according to what the constitution allows. Oligarchy: Power is restricted to a small social class, usually the wealthiest. Totalitarian dictatorship: The ruler enjoys unlimited power and controls most public and private aspects of life.