ANSWER: The Nationalists and the Communists were fighting in China for power in the China. In 1937, when Japan invaded China, the Chinese people left aside their civil war and united to defeat the Japanese. The two groups which were fighting against each other, joined hands to become a big power in the country. After the World War II, the civil war continued and stopped in the year 1949 after the Communists came into power. This is how the Japanese invasion helped unify China.
