In 1941, the Japanese navy’s aircraft-carrier task forces, which rallied at Hitokappu Bay on Etorofu Island, headed for Pearl Harbor, in Hawaii, and the Pacific War broke out on December 8. Prior to the war, in April of that year, Japan and the Soviet Union had ratified the Neutrality Pact between the Soviet Union and Japan, promising mutual nonaggression.
However, in April 1945, when Japan’s defeat seemed likely, the Soviet Union declared its intention of not extending the Neutrality Pact between the Soviet Union and Japan, which was still valid until the following year. Russia’s intent was to enter the war against Japan, which the Soviet Union had promised in secret at the Yalta Conference. On August 8 of that year, despite the still-effective Neutrality Pact between the Soviet Union and Japan, the Soviet Union suddenly declared war on Japan, and 1.6 million Soviet Far Eastern troops crossed the Soviet-Manchurian border and launched attacks. In Karafuto, on August 11, approximately 35,000 Soviet soldiers invaded across the border at 50 degrees north latitude and fought roughly 20,000 Japanese troops. A few days later, on August 14, Japan accepted the Potsdam Declaration. The war ended with Japan’s unconditional surrender.
However, the Soviet troops continued their attack even after Japan accepted the Potsdam Declaration, landing on Shumushu Island on August 18 and engaging with about 25,000 Japanese garrisoned troops. They continued advancing southward while disarming Japanese soldiers stationed in various parts of the Kuril Islands, landed on Etorofu Island on August 28, and reached Kunashiri Island and Shikotan Island on September 1 and the Habomai Islands on September 3, occupying all four northern islands by September 5.
Despite the principle of no territorial expansion espoused by the Allies in the Atlantic Charter and the Cairo Declaration, the Soviet Union issued the Soviet Union Supreme Conference Executive Order on the Establishment of Southern Sakhalin Oblast on February 2, 1946, and incorporated the four northern islands into Soviet territory. The Cairo Declaration states that Japan must be expelled from areas that “Japan has taken by violence and greed.” However, the four northern islands had never been Russian territory, and it is clear from history that this declaration does not apply.
Some of the people who lived on the islands were worried because they had lost contact with Hokkaido, and they took the risk of escaping. People who were unable to abandon their hometowns and remained on the islands were forcibly repatriated to Japan from 1947 to 1949. Since this time, Russian occupation without legal grounds has continued.