Global domination would only happen if the Germans learned how to create proxy armies like the Romans and British did. I am curious where you get the "global domination" from? Seems obvious but on reflection I'm not sure I ever heard it articulated by the Hitler. I'm not sure Britain would have fallen, America would have been forced (maybe) into the war earlier and the combination of the British and American Navies would have made the hop across the chanel difficult. Without the German army and resources tied up in Russia, invading Fortress Europe would have been considerable more difficult.