Board Thread:Administrative/@comment-24800939-20171122230252/@comment-16461120-20171123035252

It doesn't actually "split" per se, both realities simply consist of identical events up until a certain divergence, but were still always separate.

To rephrase with an example, Legion attempted to travel to the past and kill Magneto, but accidentally killed his father. Now the past that he went back to wasn't actually Earth-616 like he had intended, even though it was identical to Earth-616 up until that instant, it was already Earth-295 prior to and after Charles' death.