Just as the Imperium of Man wages Crusades against Xenos and Chaos, starting with the Great Crusade, led by the Emperor of Mankind Himself, the minions of the Ruinous Powers have launched several Black Crusades against the civilizations of the galaxy.
The Horus Heresy might be thought of as first and the biggest Black Crusade of all, when Warmaster Horus, Primarch of the soon-to-be Black Legion, led his Legion and eight others, the very first Chaos Space Marines, to try and overthrow the Emperor. They left the Imperium in ruins, but were narrowly defeated in orbit around Terra.
Abaddon's Black Crusades
Ezekyle Abaddon, Warmaster of Chaos, is the most prolific Black Crusader. He has launched thirteen Black Crusades in his ten millennia of serving Chaos, and he opens each one with the same words Horus used to launch his Heresy (which, since Abaddon is hinted to be a clone of Horus, might be retroactively called the Zeroth Black Crusade): "Let the galaxy burn!" His Black Crusades also end in the same way that the Horus Heresy did:
failure He's destroyed Cadia, and earned a glorious victory for the Black Legion. BLOOD FOR THE BLOOD GOD!
A new perspective
These constant failures have not escaped the eyes of the fanbase, and so Games Workshop (read: Aaron Dembski-Bowden) has rewritten the first twelve Black Crusades, now explaining that the first twelve were not for the purpose of conquering Cadia or Terra: they were simply aimed at gathering various superweapons, undermining the Imperium, and generally preparing for the "main event" of the thirteenth. Regardless, /tg/ tends to continue to mock Abaddon and his failures, because memes are fun and/or everything Games Workshop does is to be mocked.
A full list of what he actually did is as follows:
- 1st Black Crusade: Abaddon cemented the dominance of the Black Legion - and his rule over it by scouring hundreds of worlds in Segmentum Obscuras even though his fleet eventually had to retreat, it (allegedly) took Rogal Dorn's life to stop the crusade. He also acquired Drach'nyen from the Tower of Silence on Uralan.
- 2nd Black Crusade: Abaddon destroyed an Imperial Navy base and the shipyards on Belis Corona and cursed the planet's moon to unleash a mutagenic plague upon the planet's inhabitants in the future. Later sacked the Inquisitorial vaults on Nemesis Tessera – butchering the Imperials and freeing all the Daemons imprisoned in the fortress.
- 3rd Black Crusade: The Daemon Prince Tallomin is unleashed on the Cadian Gate. Tallomin is banished by a dozen Chapters of Astartes, after slaughtering many millions of Imperial soldiers. It was all a distraction, as Abaddon could now desecrate the tomb of Saint Gersthal on the shrine world of the same name without any resistance, thereby preventing a prophecy of ultimate Imperial victory from coming true.
- 4th Black Crusade: Abaddon assaulted the world of El'Phanor, a stronghold of the Cadian Gate. The planet was left a dead wasteland, leaving Cadia vulnerable to later attack.
- 5th Black Crusade: The one where Abaddon summoned Doombreed.
- 6th Black Crusade: Acting on a tip-off from Be'lakor (yes, the same guy from Fantasy), Abaddon allies with the Sons of the Eye, a splinter faction that had broken off from the Sons of Horus shortly after the Siege of Terra. After annihilating a Forge World with their help, Abaddon executes the Sons' warlord and forces him to watch his men pledge their loyalty to the Black Legion as he dies.
- 7th Black Crusade: Abaddon steals some Eldar artifacts from the Adeptus Mechanicus and leaves before the Imperium can muster a response. The Blood Angels try to cut off his escape but are routed. Their geneseed is used to bolster the Black Legion's numbers, courtesy of Fabulous Bile.
- 8th Black Crusade: The Black Legion engages in a ritual sacrifice known as the Skullgather. They slaughter specific numbers of people on specific worlds, and arrange the dead in specific patterns. Hundreds of adepts of the Inquisition are driven insane in trying to break the cipher, while Imperial forces are too busy pursuing Abaddon's fleet to realize what he's doing. It ends with the council of Tech-Magi being sacrificed in the gears of the Forge World Rithcarn, completing the sequence of death and pleasing Tzeentch.
- 9th Black Crusade: Abaddon musters several Traitor Legions for the purpose of strangling the power of Cancephalus, a naval fortress that acted as a base for Imperial ships patrolling the Eye of Terror for any activity. Abaddon proceeds to massacre and mutate the people of Antecanis, a heavily populated world that provided most recruits and officers for Cancephalus. The Traitors depart after having annihilated the response fleet from Cancephalus, thereby crippling the Imperial Navy's power and opening up new routes for Chaos Space Marines to exit the Eye of Terror.
- 10th Black Crusade: Abaddon assaults the Helica Subsector (of Eisenhorn fame) with the aid of the Iron Warriors, sending out some of his minor warlords as a distraction while he and Perturabo attack the Iron Hands' homeworld of Medusa. The Iron Hands barely hold on, and Abaddon and Perturabo leave after they are satisfied with what they have learned about Medusa's defenses. While technically victorious, the Iron Hands have suffered severe casualties and many of the worlds in their system have been destroyed.
- 11th Black Crusade: After binding a Daemon of Tzeentch within the oculus of his vessel in the hope that it may find new routes through the Warp storms, Abaddon gets caught in a warp storm and ends up in orbit over the planet Relorria. There the Traitor Marines encounter Orks, and a three-sided war breaks out. Abaddon takes many Orks as prisoners, after which he departs and leaves the humans of Relorria to deal with the remaining Xenos. He later discovers their connection to the warp and begins experimenting with them to see if they could be used to create Ork-Daemon hybrids.
- 12th Black Crusade: The one where he got the Blackstone Fortresses. See Battlefleet Gothic.
- 13th Black Crusade: The last event in Games Workshop's official 40K timeline, beginning on 995999.M41. Back in Third Edition, GW ran the "Eye of Terror" worldwide campaign to determine the outcome of the war. Going by the numbers of the battles sent in (admittedly not a tamper-proof measure), the forces of Chaos actually won the ground war, and the Imperium won the space war, since this was before GW had the "fuck our customers" mindset, they actually did wrap up the 13th Black Crusade... In the 18th issue of their Battlefleet Gothic Magazine. Yep, the major event that the whole setting stops at was wrapped up in an issue nobody bought. Abaddon's fleets (including the Planet Killer and a Blackstone Fortress) were crippled and he and his generals were stranded on a dozen worlds. They continued to win the ground war on most planets, including Cadia, but even if they did capture those they'd be left stuck without any way of proceeding whereas the Imperium could just virus bomb the captured worlds. Eventually GW decided that change was both terrible and terrifying, so they retconned it away. As things stand (perpetually frozen at the brink of M42), Abaddon has just launched the Crusade, overrun most of Cadia and Segmentum Obscuras and is trying to solidify his gains and rumor has it that the Daemon Primarchs are going to intervene personally, but of course we'll never know since they'll never move past it, and even if they do some sort of event, they'll just retcon it back again. (13th Black Crusade book series, beginning soon even though Magnus was spotted.)
Considering that the Necrons are getting the spotlight in Imperial Armor Volume 12, expect for the Necrons to become more involved in the 13th Black Crusade as Abaddon tries to overload the pylons maintaining the Cadian Gate. Before you scream deus ex machina (or perhaps merely deus machina), recall that early battle reports from the background material of the Eye of Terror campaign mentioned a Necron expeditionary force operating in Segmentum Obscurus almost exclusively against the Forces of Chaos (The Imperium figured this out as well and official Imperial policy was to keep their distance and let the Necrons just do their thing). Furthermore it should also be recognized that the Necrons almost certainly built the Cadian pylons and would have the most to lose, after the Imperium and the Eldar, should the Eye of Terror expand.
7th Edition Codex has indeed shown there are a large amount of active Necron Tomb Worlds around the Eye.
Trazyn the Infinite is confirmed to be on Cadia during the 13th Black Crusade. He released Inquisitor Greyfax from her tesseract labyrinth to aid the Imperial forces against the invasion and is making some sort of deal with Archmagos Belisarius Cawl. Yeah he just convinced him to blow up Cadia, its nothing. He is even fighting alongside the cadians, for some reason.
14th Black Crusade
/tg/ has gotten tired of the so-called "Failbaddon's" antics, and so somebody decided to take matters into his own hands and launched Abaddon Quest, in which /tg/ controls Abaddon's 14th Black Crusade. He's doing much better this time around (barring a few acts of sexual deviancy that even Chaos Marines found unsettling).
Minor Black Crusades
While Abaddon is the favored son of Chaos; several other Chaos leaders, like Chaos Lords, Sorcerers or Daemon Princes have launched their own Black Crusades. Usually, these minor crusades will be launched from a coalition of sorts between several chaos warbands, as few have the resources needed to launch them on their own (Think about Marines, heretics, tanks, daemon engines numbering in the hundreds of thousands and a Titan or several). However, those who have them (like Abbadon, some Daemon Princes or VERY successful Lords like maybe Huron Blackheart) also have the benefit of a centralized command and honor no pact to an external force, which sometimes lead to a more successful campaign.
These engagements pale in compraison with Abbadon's but they're far greater than your average saturday-night chaos raid. These conflicts can reach anywhere from sub-sectors, whole sectors or several; depending of the objectives or ambition of the one who put themselves in charge (usually by skullbashing) and the bloodlust of his troops. Regardless, these "minor" Black Crusades are awful events (save for Chaos, obviously) that see billions dead and war at great scale, to the point that even Astartes' plot armor barely make it and many forces are drawn into the meat grinder to halt them. However they're usually halted, or not. It depends of the mood of the gods or the importance the Militarum Command puts on them.
To finish: Have you ever played a multi-game or map campaign with your CSM army, specially with Chaos Allies? Or you and your heretic friends thought of make some use to the tons of troops that pledged themselves to you and start a war to gain the last ounces of favor needed for Apotheosis? Then congrats, you have, or are on the way to, lead your very own Black Crusade! Now go out there and smack some more loyalist ass, champ!