Answer:
Full diplomatic relations between both the US and the USSR were established in 1933, late due to the countries' mutual hostility. During World War II, both the USSR and the United States were briefly allies.
In 1950, Mao and Stalin safeguarded the national interests of China and the Soviet Union with the Treaty of Friendship, and Alliance and Mutual Assistance. The treaty improved the two country's geopolitical relationship on political, military and economic levels. Stalin's largesse to Mao included a loan for $300 million; military aid, should Japan attack the PRC; the transfer of the Chinese Eastern Railway in Manchuria, Port Arthur and Dalian to Chinese control. In return, the PRC recognized the independence of the Mongolian People's Republic.
Despite the favourable terms, the treaty of socialist friendship included the PRC to the geopolitical hegemony of the USSR, but unlike the governments of the Soviet satellite states in Eastern Europe, the USSR did not control Mao's government. In six years, the great differences between the Soviet and the Chinese interpretations and applications of Marxism–Leninism voided the Sino-Soviet Treaty of Friendship.
In 1958, guided by Soviet economists, the PRC applied the USSR's model of planned economy, which gave first priority to the development of heavy industry, and second priority to the production of consumer goods. Later, ignoring the guidance of technical advisors, Mao launched the Great Leap Forward to transform agrarian China into an industrialized country with disastrous results for people and land. Mao's unrealistic goals for agricultural production went unfulfilled because of poor planning and realization, which aggravated rural starvation and increased the number of deaths caused by the Great Chinese Famine, which resulted from three years of drought and poor weather.
There was a whole lot of Anti-Capitalist propoganda going on around this time, so yes, they were allied against the United States of America