how did chaos betray horus the emperor killed him in the end with a massive psycic attack that obliteraed his soul
Yes, yes, we've all heard the story. Horus turns traitor, declares his allegiance to Chaos, turns his brother Primarches against the Emperor, pulls an ambush on the Loyalist SMs and massacres them along with a loyal Primarch, causes a civil war that halts the Great Crusade and kills countless billions of Imperial citizens, then he sieges Terra, inexplicably lowers the shields on his ship (and his ship alone), and then personally kills his brother Sanguinius.
Enter the Emperor. Who, supposedly, sees all this (Horus a warp-twisted madman laughing over the corpse of his weakling brother while declaring his unending fealty to Chaos and his hatred of the Emperor) and still thinks Horus can be saved (not a great stretch of the imagination, the Emperor was
a cretin). So they fight, and Horus beats the Emperor to within an inch of his life, while sustaining no fatal wounds himself.
Then (and this is the really hilarious bit) in walks one random loyalist Terminator who Horus kills. And THIS is what finally convinces the Emperor that perhaps Horus is a wee bit beyond salvation? So he doesn't care about the death of Sanguinius? Or the deaths of countless billions? It was one terminator that did it. And then the Emperor insta-kills Horus, because he could have done that all along but decided that having his LUNGS RIPPED OUT isn't proof enough that Horus doesn't like daddy anymore.
Does that make the slightest bit of sense? It's Imperial propaganda. Horus killed the Emperor, then the Chaos Gods claimed his soul (he did
sell it to them). After all, they don't want to off the Emperor only to have his son take over - what's the difference between one powercrazed cretin and another? Much better to leave the Imperium leaderless and scared. Breeds better worshippers that way.
Maybe the Imperium really believes that happened. Dorn saw the Emperor's body and Horus a pile of ash, and believing that the Emperor was just a benevolent (but incredibly, incredibly
stupid) guy who couldn't accept that his son was evil made the most sense. To a moron like Dorn that'd make sense anyway. It's fairly obvious what really happened.