Germans failure to finish the British at Dunkirk. Hitler had a chance to force the British to sue for peace had they not allowed the Brits to escape. Why Hitler held back the Panzers is still a mystery.
The second part was "Operation Barbarossa" the day the Germans invaded the Soviet Union was really the beginning of the end for the Third Reich.
The
Japanese mistake was the attack on Pearl Harbor and their inability to find the US Carriers. The entire West Coast of the US would have been wide open for invasion.
