The United States uses which form of government?

A parliamentary system is characterized by a government in which the executive branch derives its legitimacy from the legislature and is directly accountable to it. In contrast, the United States employs a separation of powers where the executive branch, led by the President, operates independently of the legislature, thus ruling out this form of government.

A unitary government centralizes power within a single national authority, with any regional authorities deriving their powers from the central government. The United States, however, operates on a federal basis, allowing states significant autonomy and powers independent of the federal government, which is contrary to the principles of a unitary system.

An oligarchy is a form of government where power rests with a small group of individuals or families, often leading to a concentration of control and limited political representation for the broader population. The United States, with its democratic principles and electoral processes, does not fit this definition, as it aims to represent the will of the people through elected officials.