How did China’s relationship with the Soviet Union develop? Why were countries interested in developing friendly ties?

In 1924, China and the USSR established diplomatic relations, on August 21, 1937, a Soviet-Chinese non-aggression pact was signed, from 1937 to 1938. assist China in the struggle against the Japanese invaders, in August 1945 the Soviet Army liberated Manchuria.
China was interested in friendly relations with the USSR, since the Soviet state provided all kinds of assistance to China in the fight against Japanese aggression: Soviet specialists assisted in the creation of armed forces, supplied modern military equipment. The government of the USSR also contributed to the end of the civil war in China, proposing to conclude a Soviet-Chinese non-aggression pact and free the country from Japanese influence.
The USSR was interested in cooperation with China to maintain stable trade and economic relations, which was greatly influenced by China’s domestic and foreign policy.