Bloodied Heresy

The so-called Bloodied Heresy is the name of the internecine Chapter civil war that broke out amongst the Dark Angels' Successor Chapter known as the Bloodmoon Legion sometime in M37, when almost half of the Bloodmoon Legion renounced their vows to the Emperor and followed the Fallen Angel called Pythea in a civil war against their loyalist brethren. Though the loyalists succeeded with their newly-found Moritats, they were left severely undermanned. This Heresy caused the remaining Bloodmoon Legion forces to swear that, from now on, they would hunt down the Fallen religiously and give them no quarter once they found them.

History
"Fallen Angel. You lay upon the blood-soaked sand of your..no, OUR land. Fortresses plundered, tribes in ruin, Astartes destroyed - all to end the Heresy with which you sought to cover our homeworld. A bloody conquest having consumed hundreds of thousands, countless tribes razed to the ground, and over twenty hundred thousand impaled and burned by you and you alone to strike fear into the hearts of mortal men! What say you, heretic, monster, devil conceived from the darkest womb? WHAT SAY YOU NOW?!"

- Chief Moritat Zachaeus, to the Fallen Angel Pythea.

Before the 37th Millenium, the Bloodmoon Legion, although a part of the Unforgiven, were lacking in their hunt for the Fallen. They believed that hunting the Fallen, no matter what, came second to their current objective at hand and would seek to kill the Fallen they went after rather than interrogating them. This way of acting eventually came back to bite the Bloodmoon Legion as one day almost half of the Chapter, unexpectedly, fired upon their brethren while the entire Chapter was in Laralia Prime for the Chapter's thousand and eighth birthday. Although initially thought of as a simple rebellion, the truth was realized when the loyalist Bloodmoon Legionnaires saw that the traitors were led by a Fallen Angel calling himself Pythea. Enraged by their brethren fighting alongside the fallen, many of the Bloodmoon Legionnaires stopped controlling their Dark Devouring and chose to embrace it instead. These warriors were severed from their squads and became independent operators known as the Moritats.

With these brutal and hungry Moritats at their side, the loyalist Bloodmoon Legionnaires fell upon their traitorous kin and their Fallen Angel leader like a whirlwind of blood and fire. Carving a bloody path through their treacherous brothers, the loyalist Bloodmoon Legionnaires eventually wiped out the traitors. However, the foul Fallen Angel was still at large on their homeworld. Deciding to give him the brutal death he deserved, the Bloodmoon Legionnaires sent the very first Chief Moritat, Zachaeus, to hunt for the Fallen Angel.

Eventually found by Zachaeus, Pythea was no match for the crazed Moritat and fell before he even realized it. In his dying moments, he watched in horror as Zachaeus crouched and began dining upon his flesh in the most brutal fashion.

Though victorious, this heresy reduced the Bloodmoon Legion to less than half of their initial strength. However the Bloodmoon Legion had learned a valuable lesson from this Heresy: The Fallen were not to be ignored any longer, they were to be hunted and slaughtered without a single shred of mercy.