1855. Russia and Japan signed the Treaty of Shimoda, marking the beginning of bilateral diplomatic relations between the two countries. The Russian-Japanese border passed between the islands of Iturup (Etorofu) and Urup (Uruppu), both part of the Kuril Islands. Subsequently, Japan established control over the disputed islands of Iturup, Kunashir (Kunashiri), Shikotan and Khabomai (Habomai), while Sakhalin Island remained under joint jurisdiction.
1875. Russia and Japan signed the Treaty of St. Petersburg ceding all Kuril Islands to Japan. In exchange, Japan recognized Russian jurisdiction over Sakhalin Island.
1905. Russia was defeated in the 1904-1905 Russo-Japanese War. Under the Treaty of Portsmouth, Japan established control over Sakhalin Island south of 50 degrees north latitude (the fiftieth parallel).
1945. The final year of World War II. The Soviet Union declared war on Japan and occupied southern Sakhalin and the Kuril Islands.
1951. The San Francisco Peace Treaty between the Allied Powers and Japan was officially signed by 49 nations. Japan renounced claims to the Kuril Islands. The Soviet Union refused to sign the treaty. The government of Japan later said age-old Japanese territories, namely, the islands of Etorofu, Kunashiri, Shikotan and Habomai, were not included in the term "Kuril Islands" mentioned by the Treaty.
1956. The Soviet-Japanese Joint Declaration brought an end to the state of war between both nations. Moscow agreed to cede the islands of Shikotan and Habomai to Japan after the conclusion of a bilateral peace treaty. However, the treaty was not signed because the government of Japan demanded that the Soviet Union cede all four islands.