It was not just the soviets who played CCP and KMT. The United States did as well. The United States had limited interest in any side in china, CCP or KMT, attaining enough influence to successfully establishing a independent modern state with the ability to exclude foreign influence and allow china to act as a cohesive self-willed agent on the international stage. But the US has a lot of interest in using Chinese forces to tie down as much Japanese interest as possible, and equally importantly be able to use Chinese manpower in various schedule offensives against japan, culminating in projected invasion of japan in late 1945.
The US was none too pleased with jiang's unwillingness to commit large number of Chinese troops to major western sponsored offensives against japan outside china. The US was also disappointed by the abysmal performance if KMT troops inside china in 1944. So for much of 1944-1945, the United States sent envoys to Yan'An and constantly threatens Jiang with switching its recognition and support from KMT to CCP to pressure Jiang to kowtow to American priorities in the East Asia theater.
American double game also continued after 1945, and kept channels to CCP open and insisted upon inclusion of CCP in many high level negotiations between US and china as a way to pressure Jiang. This is something which Chinese communist party will never fail to forget in their own version of history. Indeed the back channel between the CCP and the US state department, operation behind the back of KMT, remained open until after the fall of KMT capital at Nangjing to the CCP in 1949. When the United States was prepared to switch diplomatic recognition from KMT to CCP, and give the KMT up as a list cause, while preventing the USSR from gaining a monopoly of foreign influence over communist china.
But Mao had decided by this time that despite stalin's treachery, communist China's future lay with the USSR, not USA, and spurned American entreaties. But even so back channel contact continued between the CCP and te US state department.
China likes to portray communist struggle as a struggle of the clean, honest underdog against a mighty but correct and overbearing nationalist war machine backed by the full might of the arch imperialist power if United States. But the communists would never admit just how little direct support the United States actually have to the KMT during the Chinese civil war, and how much American double dealing may in fact have hampered Jiang. It is easy to dismiss the McCarthyism canard of "who lost china". But if one really looks at all the dealings between USA and all fractions in china, it became clear the question is legitate at a deeper level. The United States had hedged its bets by playing all sides, and yet was left with almost nothing in china proper. How?
The final rupture between CCP and USA didn't occur until Chinese troops attacked across Yalu in 1950 during the Korean War.
It might be said that Stalin permitted the Korean War in apart to ensure a decisive break between CCP and USA, and ensure Mao would not have the opportunity to play the USSR against the USA for mao's benefit.
