Well in reality it was two different wars.
Japan never really had a chance to charge through siberia and lay siege to moscow.
What really made the war global is that economically, the western allies had to deal with two very distant conflicts, against very different and determined opponents.
Thankfully, AA40 allows for the historical alternatives, such as charging to moscow with japanese tanks, which they could have tried, but even in the game, it is a bad strategy.
Fighting over all those 1 IPC territories isn’t as productive as fighting over those big money islands in the south, and economics is what wins games of AA.