After the end of the Russo-Japanese War in 1905 with the Treaty of Portsmouth, the southern half of Sakhalin officially became Japanese territory, and was renamed as Karafuto, prompting an influx of Japanese settlers there.
Following Japan's surrender, 575,000 Japanese prisoners of war captured by the Red Army in Manchuria, Karafuto, and Korea were sent to camps in Siberia and the rest of the Soviet Union.