A unitary state is a state governed as a single power in which the central government is ultimately supreme and any administrative divisions (sub-national units) exercise only the powers that the central government chooses to delegate. The majority of states in the world have a unitary system of government. Of the 193 UN member states, 165 are governed as unitary states.
In a unitary state, sub-national units are created and abolished (an example being the 22 mainland regions of France being merged into 13), and their powers may be broadened and narrowed, by the central government. Although political power may be delegated through devolution to local governments by statute, the central government remains supreme; it may abrogate the acts of devolved governments or curtail their powers.
The United Kingdom of Great Britain and Northern Ireland is an example of a unitary state. Scotland, Wales and Northern Ireland have a degree of autonomous devolved power, but such power is delegated by the Parliament of the United Kingdom, which may enact laws unilaterally altering or abolishing devolution (England does not have any devolved power). Many unitary states have no areas possessing a degree of autonomy. In such countries, sub-national regions cannot decide their own laws. Examples are the Republic of Ireland and the Kingdom of Norway. In federal states, the sub-national governments share powers with the central government as equal actors through a written constitution, to which the consent of both is required to make amendments. This means that the sub-national units have a right of existence and powers that cannot be unilaterally changed by the central government.
Unitary states are contrasted with federations. An example of a federation is the United States of America. Under the U.S. Constitution, powers are shared between the federal government and the states. The Tenth Amendment to the United States Constitution reserves powers not delegated to the United States by the Constitution to the States; however, in practice, the federal government's ability to deny funding of federal programs to non-compliant states is a powerful method of persuasion.
Italics: States with limited recognition