Editing Federation (section)

===Unitary states===
A [[unitary state]] is sometimes one with only a single, centralized, national tier of government. However, unitary states often also include one or more self-governing regions. The difference between a federation and this kind of unitary state is that in a unitary state the autonomous status of self-governing regions exists by the sufferance of the central government, and may be unilaterally revoked. While it is common for a federation to be brought into being by agreement between a number of formally independent states, in a unitary state self-governing regions are often created through a process of devolution, where a formerly centralized state agrees to grant autonomy to a region that was previously entirely subordinate. Thus, federations are often established voluntarily from "below" whereas devolution grants self-government from "above".