Korea had been an outright occupied province of Japan since 1910. In reality Japan had controlled the government since 1905. The Korean Army was disbanded and the Korean language and culture were outlawed.
Exiled Korean leaders tried to get the Korean issue into debate at the League of Nations during the thirties, while in 1939 Korean units joined the Chinese against the Japanese. Japan recruited pro-Japanese units and sent them against their Korean countrymen.
While there were no formal Korean armed forces, many men were conscripted into labor battalions, and thousands of women were forced into the role of "comfort women." Many of these conscripts, men and women, were killed when the Japanese islands were attacked or bypassed and left to starve.
In Cairo in 1943, the allies made a statement of intent to free Korea. When the Soviet Union entered the war on August 8, 1945, it also made this pledge. Soviet units entered North Korea on August 12, and Allied landings were made on September 8.
The two nations agreed to halt on the 38th Parallel, which became the formal demarcation line between two governments sponsored by the former Allies, now Cold War enemies. On June 25, 1950, North Korean forces crossed the 38th Parallel, starting the three-year Korean War.