Casualty figures can be a bit deceiving if you look at simply the raw numbers.
To get a good overall feel for how things played out you need to look at how long the different parties were fighting, how many men were engaged in that fighting.
The fighting in France and the low countries (really have to put Holland and even Germany into those figures) went on for less than a year.
The Soviets and Germans, however, had been going at it hammer and tong since 22 June 1941, 3 years longer.
The Germans also had far more forces committed in the East than in the West.
The Russians truly did do most of the fighting and most of the dying in World War II. That is largely, however, a function of their geography. Had the US and Russia's map positions been changed, it's likely that the US would have borne the brunt of the German war machine.
That said, the United States was the prime mover in the other piece of World War II -- the war in the Pacific, and there it was primarily an American effort.
The British and Commonwealth were engaged around the periphery and bore the brunt of extremely heavy fighting, but the United States was the only nation on earth that was capable of prosecuting the Pacific war as it scrolled out.
What makes it even more amazing is that the US effort in the Pacific was seen as the secondary effort. The European war was given priority.