The Soviet Union played the most decisive role in the defeat of Nazi Germany in WW2

"Although I agree that Ally air-force was simply bigger in numbers and, arguably, more efficient, the Germans had advanced anti-air flak guns. A lot of these guns could also be used against tanks and could easily out-range the Ally tanks."Anti-air guns were used by tanks against all sides in certain situations. It was not that common though and was often out of desperation. Anti-air vs tanks does not seem to be a major topic. (athough without US air power, Germany could have build more tanks or anti tank guns instead of flaks)"As a result of this technology(anti-air), Allies would suffer heavy losses in air-raids on Germany."Flak gun fire was not very accurate and relied on mass fire to often hit targets by luck. The allied startegic bomber campagin started in earnest in 1943. High Bomber losses in 1943 were high not from flak fire, but from German fighters. These raids still produced signifcant damage to the Germany. In 1943 no allied fighters had the combat range to escort bombers all the way into the heart of Germany.However, these high losses would only last a year, with the introduction of the P-51 in Feb of 1944 the losses dropped and the allies gained strong air superiorty over Europe and Germany.(in addition to range the P-51 was also a superior fighter to German BF109s and Fw190s) The German luftwaffe would be hunted to extinction by the the long range P-51 that would not allow the luftwaffe to regroup or hide. The allies could still hope to achieve air superirorty over Germany without Russia by 1945. http://en.wikipedia.org..."Yet the Allies still lost significantly more men than the Germans."The allies suffered losses of about 4:3 or 2:1 (allied;german) losses on D-day, as you said 12,000 allied and 6.000-9000 Germans. But the soviets suffered much higher loss ratios and in larger battles, suchs as:The Battle of Kiev (1941), 700,000 Soviet casualties to around 100,000 Germans, Ratio:7:1Battle of Smolensk(1941) 300,000 captured, 100,000 dead soviets, mostly German tank losses(200 tanks)Battle of Moscow (1941),"Therefore, total casualties between 30 September 1941, and 7 January 1942 (for Battle of moscow), are estimated to be between 174,000 and 248,000 for the Wehrmacht(Wehrmacht reports / Moscow estimate) and between 650,000 and 1,280,000 for the Red Army (Erickson / Moscow encyclopedia estimate).", quote from http://en.wikipedia.org...The soviets also typially suffered higher casualties than the germans throughout 1942 and 1943. "Italy" and other Axis AlliesItalian forces were losing against only the UK in N. Africa in 1940. Italy was a poorly trained, poorly equipped, poor morale army.By 1943 the US had invaded italy and knocked it out of the war. Italy would then be in civil war. Germany did deploy units both to N. Afrika (famous Afrika Korps) and to Italy. Extra German reinforcements probably could not save N. Africa, sicily, and S. Italy that were all indefensible due to Allied naval superiority. Italy would likely be knocked out by the loss of so much italian territory even if Germany could send more help than it did. http://en.wikipedia.org...Overall, this means the US was responsible for neutralizing Italy, and helping keep Japan off the USSRs back, each accomplished in 1943 and 1942 and would have probably been done even without the USSR. Without the US the USSR would (or could) have faced Germany, Italy, Japan, and all the minor Axis allies like Finland, Bulgaria, Romanica, and Hungary ALONE without the US. (since UK war effort was also critically dependent on American aid)Most minor Axis allies would probably not have helped Germany against the US. Finland and Romania helped Germany largely because the Soviets took their territory in 1940. (winter war in finland, soviet annexation of Bessarabia from the Romanians)Hungary supplied no troops to the Axis in the west in 1940, and there is no strong evidence they would have. The USSR would still exist even if it wasn't in the war and would be their dominant concern. Spain conributed troops against the USSR, but not the US. Thus the US could hope to isolate Germany. "If the USSR would have not been pressuring them, the Germans would have no reason to negotiate or surrender."That is partly true, but it doesnot change important facts and the bearing of those facts on the war. First, the fact is Germans had a very different view and atitude towards the UK, and somewhat the US compared to the Soviets. The Germans respected both countries, and even wanted to be allies with them. In Mein Kampf Hitler says the UK and US are in fact Germany's natural allies. In addtion, after the fall of France Hitler offered the UK peace, which they rejected. The soviets were not only considered racially inferior, but were considered ideologically evil. This is part of why the war on the Eastern Front was so brutal. This is important. It means that had the US not been at war, those 8 million germans that surrendered would probably have been much more likely to have fought the soviets to the death, making soviet victory more difficult and less likely. Germany will also be at 100% industrial capcity because of no allied bombing, while the Russian industry will mostly be captured and lost. (and no allied supplies, planes, and tanks to help without US constirbutions)While if the US and UK fight the war, once it starts defeating Germany Germans would be more likely to surrender, and Germany itself to negotiate a surrender. (especially with the Soviets they hate so much on their eastern border even if they weren't at war, Germans and Hitler considered the USSR the real enemy, mostly) The difference is not that Germans would not surrender, they still would once they started losing, and even when not losing would be less likely to fight to the death. (there is also a lot of history of compassion between the German and allied armies in WWI, like the christmas day miracle)Don't forget that the US heavily outnumbered the Germans on the Western front, giving them a serious advantage.The Russians outnumbered the germans the entire war and suffered much worse losses. So numbers are no guarantee of succesful battles, or if they are to a limited degree. The US and Uk combined had much more manpower than Germany also, they could hope to win a war of attrition. I would also like to point out that the topic of debate is: "The Soviet Union played the MOST decisive role in the defeat of Nazi Germany in WW2".Most decisive is somewhat redundent, as the defintion of decisive already means, 'deciding or settling the issue,' which already implies it is more important than other factors, or in this case countries. Saying the USSR played 'the decisive role in defeating Germany' really has the same meaning and implications of saying 'the USSR played the most decisive role.' The USSR had the greatest impact on the war. If any one of the other Allies was "absent", the remaining would not suffer such losses in comparison to if the USSR was absent.Due to all the arguments I've listed, it becomes very hard, if not impossible, to see how the USSR might have won alone. The USSR would fight very alone against Germany and all its allies, surrounded, losing its industrial heartland, without considerable allied aid to make up for it, against a more focused gemmany, Germans coming to the very gates of moscow, and the German industry at maximum power. The USSR without the US would have to overcome all these disadvantages. The USSR came very close to defeat as it was, had the Germans held stalingrad the outcome of the war could have changed completely. (germans would get oil, and cut the USSR in half)THe US on the otherhand was impossible to 'defeat' for Germany and Japan because they could not defeat the US navy. Thus the US could not be defeated, but could possibly defeat Germany, and had the resources and strategy to do so.