Milestones in dispute

1855: Russia and Japan signed a border demarcation treaty, recognizing Etorofu as part of Japanese territory, but not mentioning the Kunashiri and Shikotan islands and the Hobamai rocks.

1904-1905: Japan gained the southern half of the Sakhalin Island from Russia after Russo-Japanese War.

1945: The Yalta Agreement between the United States, the Soviet Union and Britain stated "the southern part of Sakhalin as well as the islands adjacent to it shall be returned to the Soviet Union".