Some keys to add to this story:

1. Lend Lease.

2. Richard Sorge, the Soviet spy in the German embassy in Tokyo who informed Stalin that the Japanese would go south, not north into Siberia.

3. Midway, which preserved the Allies' Europe-first strategy.

4. British 193 Hawker Hurricanes and Matilda tanks arriving in September and October 1941, which helped defend Moscow.

5. Stalin's November 1943 Tehran toast to American war production, "without which the war could not be won."

6. Khalkin Gol: the May to August 1939 unknown war between the Soviets and the Japanese, which convinced the bloodied Japanese military that fighting the Soviets commanded by Zhukov was a very bad idea.

https://medium.com/exploring-history/wwii-mythologies-east-and-west-ab1b82774b1d