The failure to capture Moscow, Leningrad and the 6th Army loss at Stalingrad doomed the Germany to a stalemate with the Soviets that they would lose over time. Germany could not compete with the Soviets industrial capacity nor her unlimited manpower that lie beyond the Ural mountains.
As far as Japan is concerned, any attempt to invade Russia would have ended in failure. China was soaking up the majority of her armies and resources, and the Japanese had no real tank forces or AT guns worth a name. The Soviets T-34's would have sliced and diced them. And like the Germans, the Japanese supply lines would have made it difficult if not impossible to keep their armies supplied in Russia, whereas the Russkies enjoyed short supply lines. The Germans had one soldier out of five doing security against Russian partisans who were hitting supply dumps and trains.
None of the aid the US sent to the USSR prior to those defensive battles had any effect on the outcome. Now the trucks and radio equipment we sent did help transport the Russians on their drive to Berlin, but the tanks, planes, guns we and the Brits sent at great cost through the Arctic were pretty much castoffs. Most of the Russian equipment was as good or better, and the maintenance of a mixture of UK/US gear was a logistic nightmare.
There's more, but in short, we should have stayed out of Europe and let these those Socialist tyrants beat each others brains out to the exhaustion both both countries.
Britain could have stayed out too, as Hitler had no designs on England, but Churchill wanted to play toy general. But thanks to us, the Soviets took over most of Eastern Europe and we let them take Berlin and push us out of Czechoslovakia.
Conscience does not exist if not exercised
"No matter how cynical you get, it's impossible to keep up!