Japan and Russia established diplomatic relations in 1855 when they signed the Treaty of Commerce, Navigation and Delimitation, also known as the Shimoda Treaty.
Tokyo argues that its claim over the four Russian-held islands off Hokkaido — Kunashiri, Etorofu, Shikotan and the Habomai islets — has a legitimacy dating to this point.
The 1855 treaty stipulated that the border separating the two nations lies between Etorofu and Uruppu, which Japan considers to be the southern tip of the Kuril island chain. Meanwhile, the status of Sakhalin was left unresolved, allowing citizens of both countries to reside there.
That arrangement witnessed a series of minor clashes.
In 1875, Japan and Russia concluded another treaty stipulating that Sakhalin belonged to Russia while the Kuril chain was Japanese territory.
The 1905 Treaty of Portsmouth, concluded after Japan won the Russo-Japanese War, resulted in Japan obtaining the southern half of Sakhalin.
On Aug. 9, 1945, with Japan’s World War II defeat looming, the Soviet Union scrapped a 1941 bilateral neutrality pact and declared war on Japan.
Soviet forces began landing on the Kuril Islands three days after Japan’s Aug. 15 surrender.
They advanced southward and seized Kunashiri, Etorofu, Shikotan and the Habomai islets by early September. By the end of 1948, the 17,000 Japanese who had been living on the islands had either fled to Hokkaido or were otherwise evicted.
With its surrender, Japan accepted the Postdam Proclamation, which upheld the 1941 Cairo Declaration stipulating that Japan abandon all territories “taken by violence and greed.”
Tokyo argues that the disputed islands do not fall under this category because they became Japanese territory “peacefully” through the 1855 treaty.
Moscow meanwhile claimed sovereignty over the Kuril chain, which it said included the four islands, based on the Yalta accord reached by the U.S., Britain and the Soviet Union six months before the war’s end.
The agreement dictated that southern Sakhalin and the Kuril islands would be handed over to the Soviet Union in exchange for its participation in the war against Japan. Japan does not accept this because Tokyo was not party to the agreement.
In 1951, Japan signed the San Francisco Peace Treaty, renouncing all rights to the Kuril islands and the southern half of Sakhalin.
But Tokyo argued that Kunashiri, Etorofu, Shikotan and Habomais are not part of the Kuril chain and historically had only been Japanese territory. Five years later, the United States released a statement supporting Japan’s claim over the four islands.
Moscow meanwhile did not sign the San Francisco treaty. In 1955, Japan and the Soviet Union — still legally in a state of war — began talks to conclude a separate peace treaty.
But failing to resolve the island dispute, Japan and the Soviet Union signed a joint declaration the following year putting an end to the legal state of war and reopening diplomatic ties.
In the declaration, Moscow agreed to hand over the Habomais and Shikotan upon the later conclusion of a bilateral peace treaty. The document makes no reference to Kunashiri and Etorofu.