To pre-WWII Europe. Do you think that was "fine" compared with the stable, peaceful, prosperous Europe of the last 70 years? The US was a major driver of European unity after WWII. Probably partly to further counter the Soviets, but mainly, to stop the endless cycle of European wars and instability that persisted for centuries. Really since the fall of Rome.

Brexit alone I think will have little real impact on the world economy. I think it probably will be a net negative for England. Possibly an England that soon will share the British Isles with one or more other EU member countries. Who trade more freely with the EU than with their former Sovereign. Yeah, wouldn't surprise me if the net negative for the Brits turns out to be severe.