By the end of the Second Sino-Japanese War, the power of the Communist Party grew considerably. Their main force grew to 1.2 million troops, backed with additional militia of 2 million, totalling 3.2 million troops. Their "Liberated Zone" in 1945 contained 19 base areas, including one-quarter of the country's territory and one-third of its population; this included many important towns and cities. Moreover, the Soviet Union turned over all of its captured Japanese weapons and a substantial amount of their own supplies to the Communists, who received Northeastern China from the Soviets as well.

In March 1946, despite repeated requests from Chiang, the Soviet Red Army under the command of Marshal Rodion Malinovsky continued to delay pulling out of Manchuria, while Malinovsky secretly told the CCP forces to move in behind them, which led to full-scale war for the control of the Northeast.

Although General Marshall stated that he knew of no evidence that the CCP was being supplied by the Soviet Union, the CCP was able to utilize a large number of weapons abandoned by the Japanese, including some tanks. When large numbers of well-trained KMT troops began to defect to the Communist forces, the CCP was finally able to achieve material superiority. The CCP's ultimate trump card was its land reform policy. This drew the massive number of landless and starving peasants in the countryside into the Communist cause. This strategy enabled the CCP to access an almost unlimited supply of manpower for both combat and logistical purposes; despite suffering heavy casualties throughout many of the war's campaigns, manpower continued to grow. For example, during the Huaihai Campaign alone the CCP was able to mobilize 5,430,000 peasants to fight against the KMT forces.