Well then that would all depend on how many German divisions would be needed to Garison Great Britain. ( this is ofcourse based on Britain being knocked out of the war ). I would guess that most of the freed up Germans from France would might end up in Great Britain. Which still would not leave too many German divisions being moved to the East.

Also not all German divisions were at full 20k strong.... there were some with as little as half that.

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The war against Russia will be such that it cannot be conducted in a knightly fashion. This struggle is one of ideologies and racial differences and will have to be conducted with unprecedented, unmerciful and unrelenting harshness. -Adolf Hitler