A vassal state, also known as a satellite state, refers to a country that nominally enjoys complete sovereignty in international relations, but its domestic politics, military affairs and diplomacy are interfered by powerful countries. A powerful country is one, and it is usually called a suzerain. When political changes may occur in a vassal state, the suzerain will intervene by force, such as the failure of the Prague Spring due to the armed intervention of the Soviet Union; In addition, because the country is weak, a country that needs the protection of a strong country is often called a vassal state. The vassal state is a political term in modern international relations, which appeared in the Cold War period after the Second World War. With the disintegration of the Soviet Union and the end of the Warsaw Pact, international relations changed and gradually disappeared.
The government of a vassal state is often called a puppet regime. Before World War II, Manchukuo was a puppet regime fostered by Japanese aggression against China. During the Cold War, due to the confrontation between the East and the West, countries split, such as Germany split into the German Democratic Republic and the German Federal Republic, the Korean Peninsula split into two countries, the Republic of Korea and the Democratic People's Republic of Korea, eastern bloc led by the Soviet Union in the East, and the American-led democracy in the West. The Warsaw Pact countries dominated by the Soviet Union are generally understood as the Soviet Union as the suzerain country and other Warsaw Pact members as the vassal countries. These countries mainly include Mongolia, Hungary, Czechoslovakia, Romania and other Eastern European countries.