An Oligarchy is a form of a power structure where an elite group of people have the power. A Oligarchy is typically controlled by a few prominent families, and these families pass on their influence or control on to the next generation.
One type of oligarchy is a religious oligarchy. This type of oligarchy is controlled by an elite group of people who have religious control.
Another type of oligarchy is a military oligarchy. In a military oligarchy, a country or organization is controlled by those who have military control.