There is a branch of theoretical physics wherein every action in our existence branches off in consequence.
The majority of the physics community do not agree with the theory. However, the saving grace of theoretical science is that it is theoretical.
This is somewhat of the basis for DC's Else World series. But, not exactly.
The Earths of the DCU are self-contained, well, except when one Earth intrudes into another but that's not important right now. The point being that Earth 34 is not Kansas USA, so let your imagination go wild, as far as history, characterization, and all that jazz.