*Checks Wikipedia*. I think that's the concept. :) I think war would've still happened, even if Hitler wasn't around. War isn't simple causation, I think, and I don't have the expertise to discuss the complexity of it all. But yeah, it will not have been the WWII that we know.
Same goes for Batman, I think. If Bruce Wayne didn't become Batman, sooner or later vigilantism will happen in Gotham. Maybe he/she wouldn't be as trained, rich, equipped, or as ethical as Batman, but it would've happened.