I don't have much to contribute to the argument about Poland, so I'll let others continue there. But anyway, I do agree with the general sentiments the OP expresses - Americans always, for every war, seem to ignore the contributions or effects of any other powers. Another typical example is many Americans being completely ignorant of France's contributions to our own American Revolution. So in general, Americans can be quite ignorant about history and then prone to extreme nationalism (regarding internal history stuff like extermination of Native Americans too) and this applies to the world wars as well; but as others have shown in the thread such nationalism isn't exclusive to Americans either.
So with regards to WWII, it seems pretty undeniable that the heavy lifting in Europe on the Allied side was done by the Soviets. Between the US/Britain - Britain had a longer period of fighting with greater casualties and suffering while the US provided more industrial production/resources, and of course contributions later in the war. Of course it is a valid point that Stalin's rule wasn't great for his own people and Russia's previous dealings with Germany were rather awful, but that doesn't change that Eastern Front was by far the largest in the theatre, and Hitler's losses there were a huge chunk of Germany's downfall.
One other thing, seemed like a misconception somewhere earlier in the thread - all evidence points to Germany not having a real threat of an atomic bomb program of its own. If the war had continued, sure, the US could have used its bombs against Germany, but the race against the clock the Allies feared wasn't really there. Yes, they were looking into it, but from what I've read the intelligence and historical evidence from after the war showed that they weren't on the right track and wouldn't have been even close to production for a long time; even top scientists like Heisenberg didn't know it was feasible.