Your understanding of what might happen if there where no USA involvement is so simplistic. I don't normally do history and consequences of ww2 talks these days but in your case I will make an exception.
Firstly We Brits would not be talking German if the USA did not get involved in ww2. We have a thing called the English channel 22 miles of water It stopped Spanish Phillip, the French Corporal Bonaparte, and the other corporal Hitler. The only one who ever managed it was King William in 1066 On the subject of Hitler he new the game was up when his army failed to take the oil fields at Ploesti plus the blood bath at Kursk. From that point on no Fuel the end was in site. Well we Brits on our own won the air battle and that put pay to the German invasion by sea. So what would be the outcome, lets go to "Yalta" with Starlin, Churchill, and Roosevelt by then was a very sick man. Joe Starlin took advantage of Roosevelt to the point that Churchill tried to warn him but Roosevelt would not listen. Churchills warning was an Iron Curtain will divide Europe. Back to if USA did not enter the war Joe Starlin would not have stopped at Poland he would have continued with the red army all the way to the English Channel so the French would be speaking Russian and like every would be invader that 22 miles of water would put an end to their dreams of invasion, and we would still be ordering our meals in English.
And as a foot note the only thing you Americans did give the British was the bill for the lease lend and you where paid back to the last red cent.
By the way your targets for ridicule Montgomery and Churchill. Montgomery was Irish and Churchill was half American.
