Its impossible to the say that "Oh the USSR contributed 26% to the defeat of Germany." Under what circumstances would we generate that number? In terms of casualties, the USSR would have contributed the most. In terms of material goods contributed, the US would have the most. In terms of years spent fighting the Germans, the UK would have the longest. There are an infinite number of criteria you could pick, but each would be less satisfying then the previous.

And I dont even think that the premise, who contributed the most, is really even that useful. The "Big Three" were the "Big Three" because they were the only three Allied Great Powers left. All the others (ie, France) had been beaten, or had joined with Germany. But this hodgepodge of ideologically opposing nations each contributed significantly to the overall success of the war against Germany. Englands geographical position and pugnacious attitude was invaluable. The USSR tied down millions of Germans when they needed them the most. And the US made sure everybody kept the maximum forces in the field. Had any nation given in and refused to fight (and all three could have, at several points, simply given up), the war would have evolved in a radically different way. The contribution of all three was integral in producing victory over Nazi Germany.

So I think this whole "Who contributed the most?" thing is just a giant, nationalistic pissing contest. And also a way to stick it to those godless Commies.

Whats more, there were significant numbers of other nationalities fighting - Free French, Poles, Australians, New Zealanders, South Africans, Rhodesians, Palestinians, Indians, Greeks and Nepalese to name just a few.

Then we also have to consider that China had been fighting Japan long before Hitler invaded Poland.

And we have to consider the contribution of the numerous resistance movements engaged in espionage and sabotage in the occupied countries.