After the outbreak of the War of Resistance Against Japanese Aggression (1937-1945), the CPC Central Committee headed by Mao Zedong upheld the principle of independence and initiative within the united front. They worked to mobilize the masses, carried out guerrilla war behind enemy lines, and established many large anti-Japanese base areas. Most of these base areas were located in the mountainous areas in North China, though some of them were situated on the Hebei Plain and the North Jiangsu Plain. In October 1938, Mao Zedong put forward the guiding principle of adapting Marxism-Leninism to Chinese conditions at the Enlarged Sixth Plenary Session of the Sixth CPC Central Committee. During the War of Resistance Against Japanese Aggression, he published important works such as "On Protracted War," "Introducing The Communist" and "On New Democracy." In 1942, he led the whole Party in the rectification movement aimed at subjectivism and sectarianism. This helped the whole Party better understand the basic direction of integrating the universal truth of Marxism with the concrete practice in the Chinese revolution and laid the ideological foundation for victory in the War of Resistance Against Japanese Aggression and in the revolution throughout the country. In 1943, he led the army and the people of the base areas in the production movement, which helped overcome the severe economic difficulties. In March of the same year, he was elected Chairman of the Political Bureau of the CPC Central Committee. In 1945,he presided over the Seventh CPC National Congress and delivered the report "On Coalition Government." At the congress the Party formulated the strategy of boldly mobilizing the masses, expanding the people's forces and leading them in defeating Japanese aggressors, liberating all the people of China and establishing a new democratic China. Mao Zedong Thought was established as the guiding ideology of the CPC at the congress. He was Chairman of the CPC Central Committee from the First Plenary Session of the Seventh CPC National Congress till his death in 1976.
In response to Chiang Kai-shek's attempt to destroy the CPC and its armed forces following the victory in the War of Resistance Against Japanese Aggression, Mao Zedong put forward the policy of giving tit for tat for the struggle against the Kuomintang. In August 1945, he traveled to Chongqing for negotiations with Chiang Kai-shek, which demonstrated the CPC's desire for nationwide peace.