Board Thread:Warhammer 40k General Discussion/@comment-4851119-20140118095944/@comment-6078851-20140415140427

..but after they were united with their primarchs loyalties changed: the legions were still loyal to emps only because their primarchs were, which is how the heresy happened at all - their loyalty to their primarch was greater than their indoctrinated loyalty to emps, and when half the primarchs said "we 'aint following pops no more", their marines followed.