Board Thread:Warhammer 40k General Discussion/@comment-25177957-20140720052135/@comment-4851119-20140722202208

72.93.39.135 wrote:

...Also squats and ratlings aren't fractions. You need a codex to be a fraction! Well, really the Imperium is made up of several sub-factions, some of whom are "support factions" who don't operate on their own but and the Squats were basically a support faction for as long as Epic was in print

Good point about Eldar/Tau though.

Ratlings aren't Xenos, they're abhumans: mutant human sub-species who are standardized enough and close enough to baseline humans that they Imperium is okay with them. Ogryns and Squats are this as well.