the cultural revolution
The Cultural Revolution in China was a seclusion time for them. Mao Zedung was viewed as the all mighty ruler. He regulated everything. He did not want the USSR's help so he tried to copy what they had created. He was successful at his complete power, but he lost his power. He regained it and tried to never let it go again.
The US saw this as a threat since there was another communist country out there. US was cut off from China after they had backed the nationalist Chinese. They would go to the place in which the nationalists were forced out to to deal with Chinese affairs.
The USSR at first viewed this as an accomplishment, but then when the Chinese communists did not follow his orders exactly it made him aggravated. It also gave the threat of another communist form over coming theirs.
In the war effort the Chinese nationalist loss with the US was a loss, but they did not go and join the USSR making it a somewhat tie compared to a USSR win.