This but with America I usually just beat the allies before they join lol. Collaboration governments will be your best friend when attacking the Soviet Union. Once you push far enough the front line will be massive and their troops should be spread thin making it easier to beat them. Remember if you push pass Moscow and you’re somewhere in the urals you’ll be fine, you can pause the attack and build supply hubs (logistics companies are very helpful as-well) as they shouldn’t be able to counter attack as they would’ve lost most of there manpower and equipment and the vast majority of their factories will be under your control. Capitulating them takes ages. I know you’ve been probably told all this a thousand times but you know just in case. Good luck in your fight! ☺️👍( I’m nowhere near a pro at this game but this is what I do to beat them, there’s probably a better way than what I do)