They were exiles from different versions of parallel Earths.

This is Earth - but a parallel Earth, not our own.

This was explained to the reader through the notion that the two groups of characters inhabited parallel Earths.

The novel tells the story of an invasion by "aliens" who are actually a secret society of mutant humans from a parallel Earth.

To this end he contacts alternate versions of himself from hundreds of parallel Earths, and convinces them to help him.

On these parallel Earths and amongst these peoples are different forms of Me.

The trailer is set within the parallel Earth featured in this story.

This is my proposal: that hominid speciation has been driven by the transfer of populations between parallel Earths.

Our Earth is but one of many parallel Earths split off from each other by world-changing historical events.

Heading outside to look, they quickly realize that they are in London on a parallel Earth.