Hey guys, I remember seeing this question somewhere and thought it was a pretty interesting question. I personally believe that the CCP were fully responsible for the outcome of the war because if it was not for the determination of Mao, the attitude and discipline of the soldiers and the exceedingly successful guerilla warfare tactics they would have been crushed by the might of the GMD soldiers.
I would direct you here, as you might find this response from the AMA earlier in the week relevant, although it certainly isn't the final word on the matter!