Matsumae clan
Upon adoption of the 1947 constitution, Japan became the State of Japan (Nihon Koku, ). The Empire of Japan was dismantled and all overseas territories were lost. Japan was reduced to the territories that were traditionally within the Japanese cultural sphere pre-1895: the four main islands (Honshu, Hokkaido, Kyushu, and Shikoku), the Ryukyu Islands, and the Nanpō Islands. The Kuril Islands also 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. However, the Kuril Islands weren't included due to a dispute with the Soviet Union.