Russia usually counterattacks manchuria, and so, japan usually takes out every single russian force before a blitzkreig is even possible by a rogue jap tank.
Unless germany is being hammered, it is hard to be diverting forces to asia. at times, germany gets lucky enough to take minimal casualties, and take moscow by turn 4, even if you are constantly buying 8 inf.
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I’d leave more than just 1 INF in Caucases–1 INF makes it too easy for Germany to take with a minimum of losses in the counterattack–you want 'em to hafta put a few units in there so you can destroy them next turn: make 'em think twice. Also, don’t leave Soviet Far East totally unoccupied-leave at least an INF or 2 there. Same reason more or less…
Otherwise, do what Horten says… "
I’ll try leaving more, but i have seen what happens when russia leaves a single grain of rice out of karelia (at times as little as one less fighter.) I’ll try putting more in cacasus, to see what happens.