“Or we could have just let the Nazis and Soviets beat each other senseless, then the US and the Brits could have swept in after we took care of Japan.”
The thing is, if Germany had fought just the USSR, and not had to concern itself with the rest of Europe, Germany would have won that fight. In which case we’d still have to fight Germany afterwards. But, by then, it wouldn’t have been just Germany, as Germany would have been allied with Italy, Hungary, Romania, Bulgaria, anti-communist Russia, Yugoslavia and the Balkans, and probably Turkey and Persia. Look at a map: Nazi Germany would have controlled most of Europe east of the 5th meridian; all of Asia Minor; and Russia all the way east to the Pacific. And, with Germany’s alliance with Japan...well, you get the picture.
I’m not sold on Germany beating Russia that quickly, I think it would have dragged on for years, perhaps Germany controlling most of the European part, but still facing big problems from partisans behind the lines, that tied them up. It would allow the Brits time to recoup their losses, and still with most of their Empire intact, and of course America would have been fully war-prepared, and most likely with the Nazis dealing with revolts throughout their occupied territories, I just don’t see the Nazis prevailing long-term, even without our involvement.
“The German Army in fighting Russia is like an elephant attacking a host of ants. The elephant will kill thousands, perhaps even millions, of ants, but in the end their numbers will overcome him, and he will be eaten to the bone.”
-Wehrmacht Colonel Bernd von Kleist