Board Thread:Warhammer 40k General Discussion/@comment-5.65.81.205-20131002091720/@comment-3258762-20131113170257

Then again, if the Primarchs never existed then there would be no Astartes, and as such there would be no relationship with Mars, whom would probably have conquered Terra after a while. I base this on the fact that the Space Marine legions were the ones who defeated the tribes on the Moon.

I think the Heresy would have happened anyway. It would not have any Space Marines and no Titans, but it would sure as hell have a lot more Imperial Armymen, resulting in a longer struggle and even more deaths.