In the early 1930s, the Chinese communists were focused on fighting the Kuomintang, the Chinese Nationalist Party. The Japanese invasion of Manchuria in 1931 and subsequent aggression in China led the communists to shift their focus to resisting the Japanese. In 1937, the communists and the Kuomintang formed a united front against the Japanese, known as the Second United Front.
The Second United Front was a fragile alliance, and there were frequent clashes between the two groups. However, they were able to cooperate to some extent in fighting the Japanese. In 1945, the communists launched an offensive against the Japanese in Manchuria, and they were able to liberate large areas of territory. The Soviet Union also invaded Manchuria in 1945, and the combined forces of the communists and the Soviets defeated the Japanese.
After World War II, the Chinese communists and the Kuomintang resumed their civil war. The communists won the war in 1949, and they established the People's Republic of China. The Japanese were defeated in World War II and occupied by the United States and its allies. The occupation ended in 1952, and Japan became a sovereign state again.
Since then, the relationship between China and Japan has been complex and varied. The two countries have experienced periods of tension and conflict, as well as periods of cooperation and friendship. The relationship between the two countries is important for the stability and prosperity of the Asia-Pacific region.