回复：老蒋背叛了孙中山的联俄联共扶助农工的革命宗旨。

it was power struggle. CCP was not going to carry 孙中山's policies. CCP and GMD did not have common ground and they had to spilt. It was said Cultural Revolution was the continuation of this struggle, which made some sense in that Mao and few others believed power struggle needed to go on.