[CCIP]

Well the AI generally works along in its own ways and determines its own priorities, so it can do a whole variety of things - what keeps it to historical goals are, first of all, objectives (capturing certain regions gives a certain amount of points, and that's what the various powers will be after - so naturally there are areas Germany or the Soviets will want to attack or keep), and secondly various scripted events which initiate things along historical paths.

The AI will usually not do anything incredibly shocking and unexpected if you know history, at least until events develop far enough along an ahistorical path, then you can really expect anything. Generally the beginning of the war will always play out pretty similarly. It's later in the war that things can get way out of norm.