Sakhalin

Sakhalin is an elongated island lying between the Sea of Okhotsk and the Sea of Japan, separated from the Russian mainland by the Tatar Strait and from Hokkaido by the La Pérouse (Sōya) Strait. It is administered by Russia as part of Sakhalin Oblast, which also includes the disputed Kuril Islands.

The island's status was a recurring source of friction between Imperial Russia and Japan. The Treaty of Shimoda (1855) left Sakhalin (Karafuto in Japanese) under joint, undefined occupation. The Treaty of Saint Petersburg (1875) assigned the whole island to Russia in exchange for Russian recognition of Japanese sovereignty over the Kuril chain. Following the Russo-Japanese War, the Treaty of Portsmouth (1905), mediated by U.S. President Theodore Roosevelt, transferred the southern half of Sakhalin (below the 50th parallel) to Japan, which administered it as Karafuto Prefecture.

In the final days of World War II, Soviet forces launched an offensive against southern Sakhalin in August 1945. At the Yalta Conference (February 1945), the Allies had agreed that southern Sakhalin would be returned to the USSR as a condition of Soviet entry into the war against Japan. Japan renounced all claims to Sakhalin in the San Francisco Peace Treaty (1951), although the treaty did not specify a beneficiary, and the USSR did not sign it. Unlike the Kuril Islands dispute, Tokyo today does not actively claim Sakhalin.

Sakhalin is strategically and economically significant for major offshore oil and gas projects (Sakhalin-1, Sakhalin-2), in which Western majors such as ExxonMobil and Shell historically held stakes alongside Rosneft and Gazprom. Following Russia's 2022 invasion of Ukraine, Western partners exited or had their interests restructured by Russian presidential decree. The island also remains a hub for Russian Pacific military infrastructure and is closely watched in any discussion of Russo-Japanese relations and Indo-Pacific security.