The war in Europe lasted for 69 months.

The USA was not an active belligerent for the first 27 of those months and the first meaningful American deployment against the Germans came with Operation Torch in November 1942, by which time the war was already 39 months old.

By this time, the Afrika Korps had suffered an irreversible defeat at Alamein and only days later the Soviets would launch Operation Uranus, trapping the 6th Army at Stalingrad.

At this point the war was without any doubt, unwinnable for the Germans.

In Italy, the US and British Empire deployed roughly 6 Divisions each.

For D-Day and the immediate period thereafter, the Americans deployed 19 Divisions while the British deployed approximately 14 Divisions, the Canadians 3 Divisions and the Polish and Free French, a Division each, and the majority of the air and naval forces were provided by the British Empire.

Against this must be weighed the fact that the Germans had been maintaining about 180 Divisions on the Eastern Front, with the Red Army inflicting 80% of all German casualties.

Thus the Americans did not even make up the majority of the Western Allies until the last 10 months or so of the war in the European Theatre of Operations.

Now, its not of course to say that the American contribution in terms of boots on the ground was insignificant, nor to deny that American industrial output was arguably a decisive factor in the final victory.

It is however, fair to say that the Soviets did the majority of the killing and dying.

The Allied victory in World War II was just that, a team effort by the Allies. Measuring "victory" is far more than merely counting bodies. In 1937 the United States (at the height of the Great Depression) accounted for nearly 42% of the world's warmaking potential, and during the war produced more military goods than all Axis countries combined. The United States was the only nation capable of carrying out massive, protracted campaigns on opposite ends of the planet simultaneously, and American industries carried much of the burden of providing multitudes of Lend-Lease supplies to her Allies.

Then there was the peace to consider. The Soviet Union emerged from World War II a bloodied, devastated colossus. The rest of the world was not much better. America, on the other hand, was virtually untouched at home and came away the planet's largest creditor nation with the strongest economy and most formidable military. The Second World War catapulted her to the status of a global superpower, a status she retains to this day. So in my opinion I would not consider the Soviet Union to have 'won' or contributed to the global war more than the USA. Their sacrifice was awe-inspiring, but they were far from alone.

If you only consider manpower this is the case for much of the war. However one must consider more then just that.

The US sent much more then 'some supplies', they sent huge amount of supplies that Russia needed to fight an offensive war on the scale they did. Britain had sent supplies very early on and helped the Soviets win the Battle of Moscow.

Another thing is to consider that every U-Boat was the cost of many tanks and the people in them needed even more training. The German Airforce was largely destroyed by West and building the Luftwaffe was a huge investment. The same goes for Anti-Air Guns and the conventional Navy. The economic damage done by the Allied Bombing campaign was beneficial for the Soviets as well.

War, fundamentally is not about how many people you kill. It might be equally useful to bind troupes somewhere and then ignore them. Considering all the troupes that were needed to defend against invasion from the Med, plus the troupes defending the Atlantic Coastline. Later in the War you have to count all the forces fighting in Italy and defending Greece and such.

In the end these discussions are pretty fruitless. Every nation like to point to their own accomplishments and claim its the most important. Once German had France and most of Europe no nation could hope to win easily, a team effort was the only realistic way to defeat them in the short term. Once all nations were engaged and mobilised Germany was done for.

Also please remember that the US and Britain were fighting Japan with their other hand and they were part of WW2 as well.

I would take exception with you question being the relative contributions of the various nations in "WW2" in your title and then limiting it to the fight against Germany in the actual question.

Even your saying "European/Asian" is very limited. Is China not in Asia? Is India, Korea?

It is a very limited and narrow view to consider the great fight against racial extremism to have occurred only against the Germans, ignoring the fact that it also counts out Italy and the minor Axis states.

The scale of the Pacific cannot be under stated, the distance of about 1400 miles from London to Moscow is barely more than half that from California to Hawaii, with another 3800 miles to Japan. The war against Japan spanned over 50% of the Earth's surface from India to California, from Alaska to Australia. Involving on the Asian mainland numbers of troops to rival the fighting in Eastern Europe, and at sea over 50% of the extant shipping in existence.