So, it's 25 June 1940. With an unimaginable speed France, the premier military power in Europe, has been finished by Hitler. What would be the best option, in hindsight since we can not eliminate it, for Stalin?
a) Continue alliance with Hitler with present terms, with a risk that Germany attacks Soviet Union after it has replenished the losses of Western Campaign
b) Make a formal alliance with Hitler, perhaps with concessions
c) Declare war on Germany immediately. Although Soviet forces are not ready for war, and Germany can redeploy the forces to east fairly quickly, they're also depleted by the Western Campaign
d) Declare trade embargo towards Germany which will cripple their economy. Perhaps improve relations with the US in the process.
e) Something else, what?
Now, in hindsight I would choose C, although D would be good option too. How about you and why?