Abaddon - Black Crusades: In 781.M31, five centuries after his retreat from Terra, Abaddon returned to Imperial space at the head of a host of Traitors and daemons. It was the Imperium's first encounter with the newly founded Black Legion and the return of a brutal and bitter enemy many had thought lost to the graveyard of history. Since the Great Scouring, Abaddon had remained within the Eye of Terror, rebuilding the Black Legion as a vengeful reflection of its former glory. At last, the Black Legion and the other Traitors returned to realspace, the first chapter in their Long War against the Emperor ready to be written in the blood of Imperial worlds. Through alliance, threats and promises, Abaddon was able to muster the largest force of Traitor Legions seen since the Horus Heresy and took the Imperium by surprise. Worlds close to the Eye of Terror fell into mayhem and chaos as Legions descended from the sky and daemons tore their way into reality. Only Cadia, with its formidable defences, stood firm, its brave regiments fighting from the towering gates and bastions of their cities.To counter the invasion, the Imperium was forced to divert many of the newly-formed Space Marine Chapters of the Second Founding from war zones across the Segmentum Obscurus. The Traitor Legions basked in their return from the Eye of Terror, bathing in the blood of innocent worlds and filling the holds of their voidships with slaves. On a dozen planets, the Black Legion proved worthy of their fallen Primarch and the martial prowess of the ancient Luna Wolves. Abaddon had chosen his generals well, and each competed for glory as the Legion tore a bloody gouge across the stars. The Black Legion's greatest achievement was not only its brutal victories, but also the unity it had managed to forge among the Traitors and their daemonic allies. Even though the Traitor Space Marines, daemons and Heretics turned on each other once Imperial resistance had been crushed, in the presence of the Black Legion, they gave grudging respect. This was the Legion of fear and domination Abaddon had wrought, and it was to be an ominous sign of things to come for the Imperium.In what would become a festering thorn in the side of the Imperium, the Traitor Legions, often led by the Black Legion or even Abaddon himself, would repeatedly spill out of the Eye of Terror to burn and pillage entire sectors. In the light of dying stars and flaming cities, the Black Legion would indulge their hatred of the Imperium, indiscriminately killing the servants of the False Emperor and tearing down anything they saw as a symbol of the Corpse-God. During these so-called "Black Crusades", whole star systems would be destroyed in conflicts that would drag on for standard decades or centuries until, as suddenly as they had appeared, the Black Legion would retreat into the Eye of Terror, their holds filled with slaves and plunder. The Segmentum Obscurus suffered terribly in these endless wars against the fallen Space Marine Legions, but in truth nowhere was safe from their treacherous reach. This was something the Black Legion proved time and again as it cemented its infamous reputation among the armies of the Imperium as a pitiless foe.