A mixed country refers to a national alliance composed of more than two countries. According to the degree of union, it is divided into federation and confederacy. Federalism refers to a unified country composed of more than two states or states. Confederacy refers to a national alliance formed by two or more independent countries for a specific purpose. Both unitary system and federalism are a form of state structure. Of course, the Federation is the representative of the United States, and the Confederation is like the Soviet Union before the disintegration.