Oligarchy is a word for it

“An equality of property, with a necessity of alienation, constantly operating to destroy combinations of powerful families, is the very soul of a republic—While this continues, the people will inevitably possess both power and freedom; when this is lost, power departs, liberty expires, and a commonwealth will inevitably assume some other form.” – Noah Webster, “An Examination Into the Leading Principles of the Federal Constitution” (emphases in original)