in my opinion the contest of the thread is out reality: the conquest of china was one of the strongest pilars of the japanese ideology and dates back a long time before. chinese were considered sub-humans. in the minds of japanese military elite there was only asia and the new order they wanted to establish there (china+southeast asia).
Russia was not seen any more as a threat since the 1906 war and in 1941 the new enemy was america, this because US interferred with japanese plans regarding asia. the focus for japan has always been to asia.
Provided that, imagine that japanese could change their historical concepts just because hitler asked them to open a second front in russia... well, let me say that to me it sounds a little absurd (no offence)
japan could have declared war to russia (i don't deny that), but NEVER at the price of sacrifying its goals in asia.
but since this is a "what if" thread everything is allowed
