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 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 of them are governed as unitary states.
In a unitary state, sub-national units are created and abolished, 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 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.
The United States of America is an example of a federal state. Under the US Constitution, powers are shared between the federal government and the states. Its Article V states that the approval of three-quarters of the states, in either their legislatures or state ratifying conventions, must be attained for an amendment to take effect, giving the states a strong degree of protection from emasculation by the centre.
^Devolution within a unitary state, like federalism, may be symmetrical, with all sub-national units having the same powers and status, or asymmetric, with sub-national units varying in their powers and status.
^Svalbard has even less autonomy than the mainland. It is directly controlled by the government and has no local rule.