Political union
A political union is a type of political entity. They are usually made up of smaller polities. These smaller administrative divisions are usually called federated states and federal territories in a federal government. In a centralized government, they are often prefectures, regions or provinces. This form of government may be created by cession. This is usually called unionism. The United Kingdom is an example of this unionism. In other cases, it may come from political unification. This involves coercion and conquest. If states were separated after being a single states, putting them back together would be reunification. This happened when East and West Germany joined back together as Germany.  The individual constituent entities may have devolution of powers but they must still follow the rules of a central government. In a federalised system, the constituent entities usually have internal autonomy. For example, they normally have the power to setup their own police departments. They normally give the federal government power in many areas. These often include military forces and foreign affairs. The union is seen by other countries as a single political entity.