A federation (also known as a federal state) is a political entity characterized by a union of partially self-governing provinces, states, or other regions under a central federal government. In a federation, the self-governing status of the component states, as well as the division of power between them and the central government, is typically constitutionally entrenched and may not be altered by a unilateral decision of either party, the states or the federal political body. Alternatively, federation is a form of government in which sovereign power is formally divided between a central authority and a number of constituent regions so that each region retains some degree of control over its internal affairs. It is often argued that federal states where the central government has the constitutional authority to suspend a constituent state's government by invoking gross mismanagement or civil unrest, or to adopt national legislation that overrides or infringe on the constituent states' powers by invoking the central government's constitutional authority to ensure "peace and good government" or to implement obligations contracted under an international treaty, are not truly federal states.
The governmental or constitutional structure found in a federation is considered to be federalist, or to be an example of federalism. It can be considered the opposite of another system, the unitary state. France, for example, has been unitary for multiple centuries. Austria and its Bundesländer was a unitary state with administrative divisions that became federated through the implementation of the Austrian Constitution following the 1918 collapse of Austria-Hungary. Germany, with its 16 states or Bundesländer, is an example of a federation.
Federations are often multiethnic and cover a large area of territory (such as Russia, the United States, Canada, India, or Brazil), but neither is necessarily the case. The initial agreements create a stability that encourages other common interests, reduces differences between the disparate territories, and gives them all even more common ground. At some time, that is recognized and a movement is organized to merge more closely. At other times, especially when common cultural factors are at play such as ethnicity and language, some of the steps in this pattern are expedited and compressed