The Communist Party of Korea was created in April 1925 during a surge in the national liberation movement. The Communist Party of Korea (CPK) created revolutionary worker and peasant mass organizations. In June 1926 it organized anti-Japanese demonstrations. In 1927 the CPK joined into an association of anti-Japanese nationalist force. Immediately after its creation, the communist party was subjected to repression from the Japanese colonial administation. Many party leaders were jailed.
The repression plus constant faction fights led to the CPK not being an organized force of any sort by 1928. However, communists had gone underground and fought the colonial oppression. In the early 1930's, armed conflict against the Japanese colonizers begun, which communists participated in. In August 1945, Korea was liberated from Japanese control by the Soviet army and Korean revolutionary nationalist forces including the CPK. At this point, the communist party of Korea was re-established as an organized entity.
In September 1945, United States troops occupied the southern part of Korea. This splitting of Korea in two hindered the activity of CPK. On October 10, 1945, communists in the northern part of Korea territory established an organization for their area. In 1946 in North Korea, people's committees arose, agrarian reform was carried out, industry was nationalized, and other changes were made. In South Korea, the communists were aligned with the democratic movement of the masses that were against the harmful policies of the US imperialists and domestic reactionaries.
In August 1946 the North Korean communists combined with the New People's Party and formed the Workers Party of North Korea. The communists in the southern territory merged with other parties as well and formed the Workers Party of South Korea.