Imperial Armour 13: War Machines of the Lost and the Damned (2014), p21-25 — Woeful Blasphemies of the Traitor, Renegade, Heretic and Mutant

Early to Late M31 - The Wars of the Great Scouring

Following the Siege of Terra and the death of the Warmaster Horus by the hand of his father the Emperor, the Traitor Legions - the Sons of Horus, Death Guard, Emperor's Children, Thousand Sons, World Eaters, Night Lords, Word Bearers, Iron Warriors and Alpha Legion - are driven from Terra and those regions they captured during the Horus Heresy. In an apocalyptic campaign of vengeance every bit as destructive as the civil war itself, the Traitor Legions splinter and many are driven into the Eye of Terror, where even the Loyalist Legiones Astartes may not follow. Throughout this age of war, the taint of the Warmaster's betrayal is found to have left barely any world untouched and the wars of vengeance and retribution grind on for many centuries, even as the remnants of the Traitor Legions vie for ascendancy within the Eye of Terror.

[...]

013.M41 - The Death of the Witching Moon

The Forge Moon of Keziah, in the strategically vital Agathon system, falls into an unnatural eclipse during which its population is driven to murder and madness in an endless night of horror. The dread forces of the Tenebrae and Company of Misery reign as dark kings amid the nightmare, and the baleful black light of the 'Witching Moon' that Keziah has become spreads calamity and warp-tainted phenomena wherever it now falls, threatening the entire star system. The first Imperial attacks by the Astra Militarum, squadrons from Battlefleet Ultima and the Inquisition are hurled back in tatters by the madness of the black light and the warp-filled savagery of the defenders. It is only by the unexpected arrival of the Charnel Guard Chapter, accompanied by a sacred band of the Adepta Sororitas Order of the Black Sepulchre bearing the holy relic known as the Book of Counted Tears before them, that the imminent loss of tens of billions of lives on Agathon Prime is prevented, and the insanity-inducing radiance of the Witching Moon is held back. The Charnel Guard lead a fresh assault as further Adeptus Astartes including the Iron Hands, Storm Lords and Angels Porphyr, and Adeptus Mechanicus reinforcements arrive, fighting a brutal battle of tank and gunship clashes across the web of soaring metal canyons which craze the moon's surface and chamber-by-chamber Zone Mortalis actions to purge Keziah of the shadow that has befallen it. The Chaos Astartes inflict fearful losses on their besiegers before they are driven into the deeper darkness of the Warp. In the wake of their retreat, all life is purged from Keziah before it is given back to the hands of the Machine Cult for tech-exorcism and eventual reclamation.

[...]

813-830.M41 - The Siege of Vraks

Following a seventeen-year long siege in which many millions of Imperial Guardsmen and renegade militia are killed, the vital armoury world of Vraks is brought low by daemonic incursion due to the heresy of the Apostate Cardinal Xaphan. Though the Grey Knights succeed in repelling the limitless hosts of the Abyss and closing the warp gates through which they are emerging, the world is irrevocably tainted by the stain of Chaos, poisoned unto death and its planetary arsenals expended throughout the long years of constant, grinding warfare.

[...]

998.M41 - Ke'lshan Besieged

The Purge warband lays siege to the beleaguered Tau Sept world of Ke'lshan, which is recovering after a series of invasions by both the Imperium and Hive Fleet Gorgon. Their attempt to corrupt the world's atmosphere, turning it into a corrosive soup that would cleanse the planet of life, are foiled at great cost by Fio'O Sho'Aun, renowned Tau artificer and weaponsmith, whose experimental Remora throne-fighters duel with airborne Blight Drones for control of the skies of Ke'lshan.