Legion Wars

The Eye of Terror Slave Wars were waged shortly after the end of the Horus Heresy in the Eye of Terror between the various Traitor Legions of Chaos Space Marines in the early 31st Millennium. This conflict marked the final collapse of unity between the Chaos-corrupted Space Marine Legions that had fought unified under the banner of Horus Lupercal during the Horus Heresy. It also marked the transformation of the Sons of Horus into the Black Legion led by Horus' ultimate successor, Abaddon the Despoiler.

History
This conflict between the most powerful servants of the Dark Gods was started by the Emperor's Children Legion, that Traitor Legion dedicated to the service of Slaanesh, whose excesses grew more wanton and uncontrollable in the days after the Heresy. As the supply of slaves the III Legion had acquired on Terra and other Imperial worlds as they fled to the Eye was exhausted, the Emperor's Children began to assault the positions of the other Traitor Legions within the Eye of Terror, plundering their own slave stocks for use in satisfying their perverse, hedonistic whims. One of the actions known to the Imperium that occurred during these conflicts was was the Battle of Skalathrax between the Emperor's Children and the World Eaters that saw the World Eaters finally shattered as a unified Space Marine Legion. The Emperor's Children also destroyed the fortress of the Sons of Horus Legion on the world of Maeleum, leading to a failed attempt by the corrupt Emperor's Children Apothecary Fabius Bile to clone Horus and provide a new leader for the Forces of Chaos. Abaddon the Despoiler led the Sons of Horus to reclaim Horus' corpse, and destroy the primary fortress of the Emperor's Children. Following this triumph, Abaddon declared himself Horus' successor as the Warmaster of Chaos and the master of the XVI Legion. He renamed the Sons of Horus the Black Legion after deciding that Horus had simply been too weak to conquer Terra and eliminate the Emperor fo mankind. Though long, terrible, and bloody, in the end the dwindling Emperor's Children Legion faced their inevitable defeat at the hands of their fellow Traitor Legions. The Emperor's Children, like the World Eaters before them, were finally shattered as an organized Space Marine Legion and broke up into hundreds of disparate Chaos Space Marine warbands. It is said by the adversaries of those who serve Slaanesh that during the Slave Wars the Daemon Primarch Fulgrim was himself killed by Abaddon and the Black Legion, but the Emperor's Children counter that he was given lordship by Slaanesh over an unknown Daemon World of unending pleasure, its location unknown even to many of their own ranks.