Final answer:
An oligarchy is the form of government where a small group gains power not through noble heritage but through means such as military or economic might.
Explanation:
Best characterized as an oligarchy:
The form of government described in the question, where positions of power are obtained through military might, economic power, or other such circumstances, not solely through noble ancestry, is best characterized as an oligarchy.
An oligarchy is a type of government where power resides with a small group of individuals. These elites might come to power due to their financial status, military strength, or through controlling certain resources or industries, differing markedly from a traditional monarchy where power is typically inherited. It also stands apart from a democracy, where power theoretically rests with the entire population, and everyone has a say in the government's decisions. An oligarchy does not base its leadership on popular vote but rather on concentrated power among a few.