Using three or more complete sentences, describe a unitary government system.

A unitary system of government, or unitary state, is a sovereign state governed as a single entity. The central government is supreme, and the administrative divisions exercise only powers that the central government has delegated to them. Subdivisional units are created and abolished, and their powers may be broadened and narrowed by the central government. The United Kingdom, for example, is a unitary state, as its constituent countries - England, Scotland, Wales, and Northern Ireland - have no power to challenge the constitutionality of acts of Parliament. Unitary states contrast with federal states, such as the United States, in which power is shared between the federal government and the states. (The states themselves are unitary.) More than 150 countries are unitary states, including France, China, and Japan.