[pydry]

>First of all this were USSR-Japan skirmishes not war, second they did not have to worry about Japan as was shown by Soviet–Japanese Neutrality Pact of April 1941

...two years after Molotov Ribbentrop.

If they had nothing to worry about Japan it logically follows that they had nothing to worry about Hitler either as was shown by the Molotov Ribbentrop pact.

In 1939 the Soviet military was a disaster, also. It's difficult to overstate just how exposed they were.

>Furthermore historian believe that Stalin knew that confrontation w/ Germany is inevitable

They were right to be afraid.

>In summary - Soviets and Nazis were allies till 1941 -

In summary, out of fear which was entirely legitimate. Fun fact: the only difference between them and Finland is that Finland gets excused for allying to Hitler out of fear by its western allies.