"David J. Bercuson: Author, director of the Centre for Military and Strategic Studies, University of Calgary
Although the United States played the dominant role, all three major Allied countries were necessary to victory in Europe. The most important contribution made by Britain was to survive Hitler’s onslaught in 1940. Had the British failed to hold off the Nazis, the Second World War would have taken a far different turn. Britain also played key roles in North Africa and the Mediterranean. The Soviet Union suffered greatly. But the Soviets killed far more German soldiers than rest of the Allies together. It was American industrial power, however, that proved crucial in the balance. American factories turned out more airplanes, tanks, ships and shells than Britain and the USSR combined, allowing the Americans to defeat Japan virtually singlehanded and play a huge role in the victory over Nazi Germany."
"Marc Milner: Author, director of the Brigadier Milton F. Gregg Centre for the Study of War and Society, University of New Brunswick
You can’t credit one element—or one player—with winning such a complex global war. Russia might not have survived the initial onslaught without British tanks defending Moscow in December 1941, or won great battles in 1944-45 without American industry and the role the Allied bombing offensive had in distracting German manpower and resources. There would have been no war to win if the British had not stuck it out in 1940-41, and carried the burden of the blockade, fighting and bombardment in the west in 1942-43. The massive American armies that finally swept into Germany came from the west. Then there is Germany itself, which contrived through arrogance, incompetence, brutality and genocide to lose a war it ought to have won easily! The united nations beat Germany and its satellites."
There are dozens more similar to this one. I can find historians that credit each of the three as the major contributor to the fall of Nazi Germany. It all comes down to the opinion of what contributed the biggest impact. They all have valid claims. From a military perspective, "I" still stand by the US's supply contributions in addition to the bombing runs that destroyed Germany's economy and distracted troops and air support away from the Eastern front to defend Germany. Their production changed from bombers to fighters, which weren't as effective as they had hoped. The Soviets hosted the lion's share of the fighting. They lost way more people. They were inferior in tactics and arms. They held on long enough to start winning the production war and turn the tide with the help of the distractions from the West that recalled soldiers/air support and crippled the Nazi economy. It is what it is though. You can't dismiss Britain's contributions either. Whatever. I'm going to sleep. Seriously though, we need to move this to its own topic if we are going to continue