from the southern part of Korea. The number of Koreans in Japan in 1930 was more than ten times greater than that of 1920, reaching 419,000. However, the jobs they could get on the mainland of Japan were curtailed by open discrimination and largely limited to physical labor due to their poor education; they usually worked alongside other groups of ethnic minorities subject to discrimination, such as burakumin. Before World War II, the Japanese government tried to reduce the number of Koreans immigrating to Japan. To accomplish this, the Japanese government devoted resources to the Korean peninsula. During World War II In 1939, the Japanese government introduced the National Mobilization Law and conscripted Koreans to deal with labor shortages due to World War II. In 1944, the Japanese authorities extended the mobilization of Japanese civilians for labor on the Korean peninsula. Of the 5,400,000 Koreans conscripted, about 670,000 were taken to mainland Japan (including Karafuto Prefecture [present-day Sakhalin, now part of Russia]) for civilian labor. Those who were brought to Japan were forced to work in factories, in mines, and as laborers, often under appalling conditions. About 60,000 are estimated to have died between 1939 and 1945. Most of the wartime laborers returned home after the war, but some elected to remain in Japan. 43,000 of those in Karafuto, which had been occupied by the Soviet Union just prior to Japan's surrender, were refused repatriation to either mainland Japan or the Korean Peninsula, and were thus trapped in Sakhalin, stateless; they became the ancestors of the Sakhalin Koreans. After World War II Koreans entered Japan illegally post-World War II due to an unstable political and economic situation in Korea, with 20,000 to 40,000 Koreans fleeing Syngman Rhee's forces during the Jeju uprising in 1948. The Yeosu-Suncheon rebellion also increased the illegal immigration to Japan. It is estimated that between 1946 and 1949, 90% of illegal immigrants to Japan were Koreans. During the Korean War, Korean immigrants came to Japan to avoid torture or murder at the hands of dictator Syngman Rhee's forces (e.g. Bodo League massacre). Fishers and brokers helped immigrants enter Japan through Tsushima Island. In the 1950s, Japan Coast Guard secured the border with Korea, but apprehending illegal immigrants was difficult because they were armed while Japan Coast Guard was not due to the terms of the surrender of Japan after World War II. During this period, one-fifth