Board Thread:Questions and Answers/@comment-12959254-20150224153902/@comment-1038387-20150224155024

Crisis on Infinite Earths wasn't the first crossover, there were plenty of Pre-Crisis Multiverse Crossovers. They also had tons of what-if stories. What if Superman and Batman had kids? What if Lois married Luthor? These were dubbed "Imaginary Stories", many of them were later retconned as alternate universes, but weren't originally. They're just entertaining stories to entertain kids that didn't bother with continuity.

The main multiverse, however - Earths One, Two, Four, S and X, essentially boiled down to characters from different companies living in their own universes. They crossed over because, hey, if you can get a Captain Marvel fan to pick up a Justice League comic by having him crossover, that's a bonus. And vice versa. Earth-Three was the only derivative alternate universe, a mirror universe.

COIE was a tool to get rid of it all. But then, as the years went by, people realized how much they loved the Multiverse, either as evil versions, or What-if... Elseworlds. Hypertime was invented to account for it, to have a multiverse without having to use the world Multiverse. They just gave up pretending with 52.

I'm not sure who has more alt earths, Marvel or DC. Marvel, at any rate, has a better way of ordering them. DC had three multiversal reboots now, it quite made a mess of things.