despotism -
Government by a singular authority, either a single person or tight-knit group, which rules with absolute power.
Wikipedia
Despotism is a form of government in which a single entity, called the 'despot', rules with absolute power. That entity may be an individual, as in an autocracy, or it may be a group, as in an oligarchy. The word "despotism" means to "rule in the fashion of a despot" and should not be confused with 'despot'.