Matsumae clan
Japan has a longstanding claim of the Southern Kuril Islands (Etorofu, Kunashiri, Shikotan, and the Habomai Islands). These islands were occupied by the Soviet Union in 1945. The Kuril Islands historically belong to Japan. The Kuril Islands were first inhabited by the Ainu people and then controlled by the Japanese Matsumae clan in the Edo Period. The Soviet Union did not sign the San Francisco Treaty in 1951. The U.S. Senate Resolution of April 28, 1952, ratifying of the San Francisco Treaty, explicitly stated that the USSR had no title to the Kurils. This dispute has prevented the signing of a peace treaty between Japan and Russia.