User blog comment:DirgeOfCerberus111/An Alternate Universe? Let the heresy begin!/@comment-2253300-20110824124948/@comment-3562230-20110825214110

So, I was thinking that since some of the primarchs landed on worlds that had medieval technology they never would have made it to space and formed their own empire. Khan and Leman Russ for example, would be supreme overlords over their respective home worlds, but probably never would have left the surface.

Of course they could have been discovered by eldar or something who gave them space tech.