The correct answer to this open question is the following.
All decision-making power concentrated in a council made up of high-ranking members of the military is an example of an oligarchy.
An oligarchy can be defined as the control of a small group that rules a country or a company. In the case of the military, the way it operates is similar to an oligarchy where a small hierarchy of generals lead the Army, Navy and the Air Force. Nonetheless, the President of the United States is the Commander in Chief of the US Armed Forces.