Well, in response to the comments, what happened was that the USSR was preparing to seize Bessarabia, and the bulk of their land units were deployed there. Because US entry was so low, the Soviets kept their force in place for when the entry got higher ... they knew that the Germans would deny the claim entirely if there was no force there.
So they did not have time to move forces from Bessarabia to Poland to up the garrison value (bear in mind the Germans attacked in Mar/Apr 1940, only the fourth turn of the game, so there wasn't even time to assemble many new units.
Anyway, back to the war!
Here is global control at the start of Sep/Oct 1940:

"Look at you - you have HORSES! What were you thinking?!?" - Paratrooper David Webster