Because he rules People "rule" lines - Wikipedia
It's called an oligarchy
An oligarchy is a government ruled by a small number of people. It comes from the Greek words oligos ("few") and arkho ("rule").
An oligarchy is a system of government controlled by a small number of people. These people are often part of a small clan, clique, or organization.
The basic idea of 'faction before blood' was incorporated within the story when Tris is troubled and confused whether to be on the Dauntless' side or the her original faction, Abnegation's side. Someone then tells Tori that 'faction over blood' was the general rule. Of course, it's Tris, so she doesn't follow the rule and believes in something else. But this idea of 'faction over blood' creeps her out.
It is called a triumvirate.
the rule of a small group of people
rule by a small group of people
Rule by the people is called a Democracy. Rule where the people elect representatives is called a Republic. Other common types of government include the following: Monarchy: rule by a king or queen Aristocracy: rule by aristocrats (usually the wealthy, educated people) Autocracy or Dictatorship: Rule by one person or a group of people. (Although of course most dictators claim to be leaders of democracies.)