evidence: Sakhalin Oblast (Russian: Сахали́нская о́бласть, romanized: Sakhalinskaya oblast', IPA: [səxɐˈlʲinskəjə ˈobləsʲtʲ]) is a federal subject of Russia (an oblast) comprising the island of Sakhalin and the Kuril Islands in the Russian Far East. The oblast has an area of 87,100 square kilometers (33,600 sq mi). Its administrative center and largest city is Yuzhno-Sakhalinsk. As of the 2021 Census, the oblast has a population of 466,609.[10] [...] In 1855, Russia and Japan signed the Treaty of Shimoda, which declared that both nationals could inhabit the island: Russians in the north, and Japanese in the south, without a clear boundary between. Russia also agreed to dismantle its military base at Ōtomari. Following the Second Opium War, Russia forced the Qing to sign the Treaty of Aigun and Convention of Peking, under which China lost all territories north of Heilongjiang (Amur) and east of Ussuri, including Sakhalin, to Russia. A Czarist penal colony was established in 1857, but the southern part of the island was held by the Japanese until the 1875 Treaty of Saint Petersburg, when they ceded it to Russia in exchange for the Kuril islands. After the Russo-Japanese War, Russia and Japan signed the Treaty of Portsmouth of 1905, which resulted in the southern part of the island below 50° N passing to Japan; the Russians retained the other three-fifths of the area. South Sakhalin was administered by Japan as Karafuto-chō (樺太庁), with the capital Toyohara, now known as Yuzhno-Sakhalinsk.