Reposting this so people stop faffing around with unimportant tangents and actually address the HH timeline so we can a) make the changes we need and b) fucking get away from the Primarchs:
>Horus being resurrected by Erebus at the Serpent Lodge
Erebus is killed for being tainted by Chaos. Alternatively, Horus is never accepted into the lodge because she's a woman. Since Sanguinus is our Arch-Traitor, whatever happens to turn him happens here.
>Pertuabo destroys Olympia
Persephone does not destroy Olympia. Working with Corax, he has the bickering lords assassinated, and assumes direct control. Her homeworld secure, she does not fall to Chaos.
>Horus rallies his allies (Fulgrim, Mortarion, Angron, Konrad Curze, Perturabo, and Alpharius)
Sanguinus slowly turns Rogal Dorn, Morticia, Loraine, Agna, Alpharia & Omegon, Lion El`Johnson, to Chaos. Magna remains on the fence.
>Blood and Dark Angels are sent away to prepare for the rebellion
Since these are both Traitor legions, there is no reason for this to happen.
>Burning of Prospero
Lara and Magna clash over sorcery. Lara breaks Magna, and she reaches out to the dark gods. The Thousand Sons are transported to the Eye of Terror.
>Battle over Alaxxes
Alpha Legion assault the Wolves. Lara is wounded and on her ship. Lion suddenly warps in with his fleet, blasting Alpha Legion and Space Wolf alike. He goes after Lara, but she slips through his grasp. The remaining Space Wolves fleet warp away to Fenris to lick their wounds
>Isstvan, open rebellion declared
Sanguinus (and whoever we decide to participate in this battle) obliterate the remaining loyalists in their Legion. Their fall to Chaos complete, they begin plans to invade Terra. Salamanders, Iron Hands, and Raven Guard nearly meet their demise at this battle (could rework some of this?)
>Schism of Mars
This is completely untouched territory, we need to hammer this out.