Jim Lacey, a professor of strategic studies at the Marine Corps War College, has a superb essay on Operation Barbarossa, which was Hitler's invasion of Stalin's Soviet Union. The National Socialist Fuhrer and State Atheism's 'Papa Joe' had been allies until Hitler's betrayal, both happy to carve up Poland and to advance designs on the innocent slavic nations unfortunately located in their path. Operation Barbarosa ended that entente, and cost the lives of 25 million Russians, mostly civilians.
Hitler's hubris ended the Thousand Year Reich 988 years early. The Soviet Union, mankind's most ambitious experiment in State Atheism, limped on for 46 more years before it collapsed.
I pray that we never see the likes of either of these monsters of the Left-- National Socialism or International Socialism-- again.