Who or what was responsible for the Sino-Soviet conflict?
The main cause of this split was the simple fact that these were two countries that bordered on one another and each wanted to be a great power.
Because of this fact, it is not surprising that there were border disputes between the two sides. The border disputes went back centuries to a treaty that had been imposed on China when it was relatively weak and the Russian Empire (as it was at the time) was very strong. As China aspired to become a great power in the 20th century, this was bound to arise as an issue.
If it had not been for this conflict, the issue of ideology would have been much less of a problem. If the two countries had generally gotten along well, a dispute between Mao and Khrushchev over Marxist doctrine could have been papered over. But because there was already a conflict between the two over national interests, the ideological dispute came to be important.
In general, then, this split was caused mainly by the fact that these two countries each wanted to be a major power and therefore had somewhat conflicting interests in some areas.