system
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human
[WH40K]What's the deal with Alpha Legion?

I know the Alpha Legion primarchs were acctually loyal to the big E despite there betrayal. So what's up with that now? Are those primarchs dead? Has the Alpha Legion truly turned to Chaos?
gpt
Nobody knows for certain.

The Alpha Legion did turn traitor, but it'd be more accurate to classify them as renegade. Alpharius and Omegon betrayed the Imperium not because they were seduced by Chaos, but they were shown a vision by a group of xenos called the Cabal. This vision showed two possible futures for the Horus Heresy.

1. Horus wins, and the galaxy burns as Chaos goes to town on the quadrillions of souls with nothing to stop them. However, a spark of Horus's morality and honor would eat at him non-stop. This would send him down a self-destructive path and create conflict amongst the traitors who had helped him. Only ending when humanity is completely annihilated a few centuries later. But Chaos would've sank it's teeth into humanity so deeply, the destruction of humanity would erase Chaos from existence. Leaving only an empty Warp.

2. Horus looses, and it creates the modern 40K universe. The emperor is forever trapped between life and death on the Golden Throne, and humanity slowly implodes on itself. Chaos would only grow until it overran the entire universe.

The twins believed the in the lesser evil and chose to support Horus and destroy Chaos. However, this plan backfired spectacularly when Horus was killed. Now the legion was caught in limbo; they seek only to destroy Chaos but they're also the enemy of the most powerful faction in the galaxy.

As for the primarchs, nobody knows if they're dead or not. Roboute Guilliman, Primarch of the Ultramarines, claims he killed Alpharius personally. But there have been multiple claims Alpharius or Omegon, or both are still very much alive and Guilliman's victim was a decoy. This rumor was only furthered enforced when the Imperium discovered the Alpha Legion not only survived but prospered. Swelling to a force complete with a massive battlefleet, standard infantry, and possibly hundreds of thousands of marines.