So if Germany had proceeded with operation Sealion - invasion of Britain- and succeeded, but not with operation Barbarossa - invasion of soviet union, could they not have won? There would be nowhere in Europe for North Americans to muster and USA would likely remain neutral (pre Pearl Harbor). Germany would get British colony oil and only have to defend against Soviet attack.
The battle of Britain was a very close thing and if the Germans had used a slightly different strategy, they could have won. Given that America was not yet in the war and there was an alliance with the Soviet Union, could you explain why the Germans could not have proceeded with operation sealion bearing in mind that the allies did essentially the reverse 4 years later?