Kimberly - here is common sense. Did Royal Navy squashed Germany in the sea? Did they sink Bismark? Tirpitz? They sure did!
Did Royal AirForce (also a joke, but less of a joke than Luftwaffe) win the Air War against Germans in 1940? They sure did!
So, it's not even multiple nations that are needed.
Then Hitler (out of desperation) attacks Russia. He gets lucky - Stalin was ready to strike and didn't have much of defense. In addition, Russian people didn't even want to fight for Stalin and his commies. So, by pure luck, Germans make good advances. By August, these advances end - Germany is out of fuel, out of parts.
That's all Wehrmacht was good for - 1-2 months of fighting in a nice summer condition.