Scipio I just noticed above you saying "I never claimed the US defeated the Nazis" .... I missed this initially. It's good to actually read that!
The problem and argument arose in your initial post #3 above with sentences like:
"What did the US get out of defeating the Nazis"
and
"The US defeated the Nazis to help our allies"
Going by your later comment above you obviously didn't intend to imply the US defeated the Nazis alone. Therefore I shall now reframe from being 'anti-American' in my comments! I do recognise the vital part in the war played by the USA ... just as vital in the final defeat of the Nazis as Britain and Russia's contributions.
The assertion the US could have defeated the Germans alone if everyone else had surrendered and only the US were fighting them necessarily admits that the US did not defeat the Axis alone.
Could have means didn't happen but would have been possible by definition.
So I still don't understand how you thought I was claiming the US won the war alone. Particulary comments like "US casualties would have been higher if the US had to fight alone"
I still think your assertion the USA could have invaded Europe alone and defeated the Nazis is quite ludicrous. But the argument depends on what Germany you would be attacking; if it was the German army of early '45 decimated by the losses on the Eastern Front and D-Day landings and The Battle Of The Bulge and with Italy having switched sides then yes you probably could have defeated them at a huge cost.
But if it was the battle hardened fanatical Germans who swept aside France and the BEF in 1940 and poured into Russia you would have been decimated on the beaches. Experience of battle conditions is obviously vital; in any battle green troops against battle hardened divisions is a complete mismatch. Any American invasion would obviously be with completely raw troops with inexperienced commanders and I think you know how difficult it would have been.
I guess you don't realize how much smaller the 1940 and 41 German military was compared to in 1944. The 1944 military was much more capable than the 1940/41 era. Taking half of Poland the Germans suffered rather high casualties. The tanks of that era were much less capable than the Panthers and Panzer IVs in Normany. Their aircraft less capable as well. The advances in their tanks and aircraft happened only because they were actively at war. Germany was ready to halt tnak production completely upon Soviet surrender and ramped tank production down towards late 1941. They had to ramp it up and get on a floor footing because the US helped keep the Soviets in the War.
You grossly overestimate the size and effectiveness of a force the US would have faced had the US opposed Germany alone. You also grossly overestimate the skill of the early German forces, they were good but not significantly better than those around in 1943 and 44 that the Western Allies fougth in Italy and France.
The least efficient military was the Soviet military. They didn't care about losses, forcing men to stand ground and fight or be shot by their own forces above all caused the enormous casualties they suffered. They suffered enormous losses in 1941 but continued to suffer large losses in 1942. Some of their largest losses were during their offensives though. They used numbers in lieu of skill. They didn't suffer huge losses because they faced tougher Germans than others. They used inferior tactics which some say are not inferior because they did work but which people who care about minimizing loss of life consider inferior and reckless like wasting 100,00 lives just to clear Berlin.
What did all that blood accomplish? It didn't help the people it helped the Soviet government instill puppet regimes and to annex land from various countries like Poland. Churchill warned of such but FDR thought he had Stalin around his fignger and had communist sympathizers in his cabinet and never took a post war hard line like should have been done. Churchill wanted to invade through Italy or the Balkins so that the Soviets would be prevented from seizing Eastern Europe but FDR refused to support it.
FDR prevailed because over 80% of the Western forces were American so it was obvious who had the leverage to call the shots and who didn't.
The bottom line is that the US facing the German military of early 1942 in France would have featured the US having far more tanks, and aircraft an more men as well because the German Army in 1942 was smaller than in 1944. The entire 1942 military was larger than the number of troops that were in Italy and France in 1944 but not all of it would have been in France during an invasion and the US could have invaded other areas instead.
Most of the 1942 force oculd have been transferred to fight the US but not all of it because they still needed forces to garrison the gains they made elsewhere including huge swaths of Soviet land. The US could have landed a 6 million man force and expanded that to 10 million if needed. The Germans would have not been able to match our numbers and at some point would have been forced back as they were historically. But atomic weapons again would have ended things sooner. Especially since they would not have wanted to have their military be totally destoryed by the US in which case the Soviets could easily annex Germany.
The Soviets would not have used peace to do nothing, they would have built up their military to eventually prepare to try to retake lost land.
Total war is a battle of attrition not a sprint where 1 battle can detemrine the entire outcome unless that one battle features losing a large percentage of your population or industrial base and thus inhibits your ability to make war.
The US industrial base and population represented 50% of the World's military potentional at the time. That means the US had the ability to field the largest Army and air force. The US Navy and our shipbuilding potential means the US had the ability to transport and supply that force abroad.
That is what matters in assessing the ability of one country to defeat another in a war of attrition.
Germany didn't lose WWI because its soldiers were inferiro it lost because the Allies even without the Russians still had a larger population base than Germany and the industrial might to field a larger force. With Russia knocked out the Germans actually had an advantage in numbers but the US nullified that advantage. There was nothing the Germans could do to defeat the Allies they could win an individual engagement here or there but in total war had no hope and that was why they surrendered. Their firlded force was not able to prevent an Allied advance into Germany. They lacked the ability to prevent it the same way the Germans would have lacked the ability to prevent the US from invading Germany if the US had chose to send enough men to Europe to accomplish it.
They were smart and surrendered before total destruction of the German Army and occupation of Germany which would have followed.
It is hard to say if Hitler would have been as stupid or willing to give up Western Europe to keep the gains in the East. But the atomic bomb would have resulted in destruction to the point that Germans would not have had the stomach to fight anymore and would have revolted probably if he insisted on Germany being turned into a radioactive wasteland.