Throughout the Cold War, the Soviet Union and China competed for influence in Asia, for example in the Cambodian-Vietnamese war that began in 1975. China was also opposed to Soviet moves in Afghanistan, believing that the Soviets were trying to surround China.
Despite the fact that the USSR and China were the two most notable communist regimes after World War II, the countries' different stages of development created an ideological gap, which manifested very early on in the Sino-Soviet relationship. On the one hand, the relationship with the Soviet Union was very important for the fledgling People's Republic of China. Chairman Mao Zedong only made two trips abroad during his time in power, in 1949 and in 1957, and both of those visits were to the Soviet Union. In the early 1950s, after Mao took power from the nationalists, the Soviet Union guided China as it pursued a centralized economy focusing largely on heavy industry.
However, Mao was increasingly disillusioned with the Soviets, believing that traditional Marxism was intrinsically European and had to be adjusted to fit non-European societies. By the late 1950s, Mao's attitude towards the Soviets could be summed up by this statement to fellow Chinese Communist Party members: "I couldn't have eggs or chicken soup for three years because an article appeared in the Soviet Union which said that one shouldn't eat them. Later they said one could eat them. It didn't matter whether the article was correct or not, the Chinese listened all the same and respectfully obeyed. In short, the Soviet Union was tops." China's development strategies also changed, as it began to focus on the mass organization of peasant labor to make the Great Leap Forward - which would have disastrous effects for China. It was also in many ways a Great Leap Away from the Soviets.
China and Russia are both powerful nation-states whose power and influence is proportional to the amount of national pride each population feels about its country. But they are also very different, separated geographically by formidable distance and barriers, and with different strategic priorities. Though recent international developments have brought Sino-Russian relations to a relatively high point, there are still plenty of stumbling blocks to the further advancement of those relations and geopolitical constraints stifling a super alliance that could theoretically challenge U.S. power. Perhaps the single element that the two countries have most in common is that both face very serious internal issues - foundational challenges that we forecast will lead to their obsolescence as regional powers over the next 25 years. Neither can help the other avoid those forces. Misery in this case cannot abide company.