China is only my second PhD field, but here's what I know; Mao never particularly liked taking orders from the Soviets, but both Stalin and Kruschev treated him like a subordinate. In addition, the Communist Party of China has always had a bit of a nationalist element to it (not so different from, say, the Viet Minh) and the Chinese had some outstanding territorial issues left over with the Russians from the bad old days of 19th century gunpoint diplomacy.

To cap things off, Maoism is ideologically distinct from Soviet Marxism, which led to the two parties vying for influence over global communist parties.

This led to a brief and indecisive shooting war in 1969, which in turn prompted Mao to begin thinking about how to counter threats from the Soviets. And when you wanted to counter the Soviets back then, there's really only one place to go to: good ol' Uncle Sam.