The Potsdam Declaration explicitly named four main Japanese islands in its sovereignty terms.
The declaration stated that Japanese sovereignty would be limited to Honshu, Hokkaido, Kyushu, Shikoku, and such minor islands as the Allies determined. The count of four refers to the four named principal islands, not to every island belonging to Japan. The wording also left the status of additional smaller islands to Allied decisions.
These four islands form the geographic core of the Japanese archipelago. Honshu is the largest and includes Tokyo, Kyoto, and Hiroshima. Hokkaido lies to the north, while Kyushu is the southwestern main island and Shikoku is the smallest of the four principal islands.
The declaration also required Japan to withdraw from territories seized during its imperial expansion, including Korea and Taiwan. Its terms drew on earlier Allied statements, especially the Cairo Declaration. The Japanese Instrument of Surrender later required Japan to accept and carry out the Potsdam Declaration’s provisions.