The War of the False Primarch was a conflict fought by the forces of the Imperium of Man in 860.M33. During the War of the False Primarch, a dark and bloody episode in the Imperium's history now largely lost to myth and purged from all Imperial records, the Segmentum Pacificus was plunged into anarchy, and the "Pentarchy of Blood" was convened by the High Lords of Terra to enact their judgement.
Five Space Marine Chapters (the Flesh Eaters, the Carcharodons, the Charnel Guard, the Death Eagles and the Red Talons) were unleashed to systematically destroy eleven other Chapters of the Adeptus Astartes judged Traitoris Perdita and lay waste to their homeworlds, finally drawing the eight-solar-decade-long conflict to a close.
- Imperial Armour Volume Two, Second Edition - War Machines of the Adeptus Astartes, pg. 17