The Crimson Path is the overall strategic plan of Abaddon the Despoiler, the Warmaster of Chaos and Chaos Lord of the Black Legion, to lead the Forces of Chaos from Cadia all the way to Holy Terra itself in the final days of the 41st Millennium. Abaddon intends to succeed where his predecessor Horus failed, breaking the Imperial Palace wide open and tearing the Emperor's rotting corpse from the Golden Throne. The Despoiler has proven himself beyond any doubt, for he is the chosen champion of the Chaos Gods, and he has spent many standard years calling in old alliances, striking daemonic bargains and invoking ancient pacts with the Traitor Legions. Thread by tenuous thread, he has woven a web of allegiance that unites the scattered and maniacal planets of the Eye of Terror under his banner.
Abaddon is confident that he can eventually smash open the Cadian System and flood into Segmentum Solar with an unprecedented number of Chaos warships. But driving his invasion across the stars to Terra is another matter -- such an act would spur so many Space Marine Chapters of the Adeptus Astartes to marshal against him that the Crusade would be forced into a stalemate. As tempting as a grinding, brutal war of attrition is, it cannot be allowed to come to pass. Instead, Abaddon is throwing his might into the Cadian Gate. His plan is for his warriors to bring about so much death and destruction that his daemonic allies can breach realspace wherever they wish and be sustained indefinitely by the unbridled mayhem that rages around them. The demolition of the strange black monoliths that dot Cadia's surface is a priority; every augur and omen Abaddon's Sorcerers have consulted suggested that these pylons are instrumental in holding open the Cadian Gate. Once the daemon legions begin to spill out of the Eye, the protective perimeters of Cadia will be breached forever, and all the manifold armies of Chaos will be free to pour into realspace like blood from a deep wound. In short, Abaddon intends to tear open the gates of hell.
By launching his 13th Black Crusade, the Despoiler hopes to achieve his ultimate goal. Those Traitor Legions and Renegade Chapters who have sworn allegiance to the Warmaster of Chaos are forming the vanguard of the invasion, a broad-headed spear to plunge deep into the heart of the Cadian System. As the Crimson Path drives ever closer to the heart of the Imperium, the devastation they cause will allow even the most powerful beings, such as the [[Daemon Primarchs, to re-enter realspace, sustained by the carnage wrought by Abaddon's vanguard. Once Cadia is reduced to ruin, the Eye of Terror itself can be drawn onward by the irresistible pull of Chaos, spilling out behind the advance of the 13th Black Crusade until it stretches towards the holy seat of the Emperor Himself. Meanwhile, dozens of the Renegade Chapters that lurk in the Maelstrom will pour out into the Segmentum Solar, forcing the Loyalist Space Marines to spread themselves thin as they fight a war on dozens of different fronts.
Abaddon's plan is of such unimaginable scale and ambition that it could only have come from a visionary leader. It may even yet come to pass. If the Despoiler is successful, the Warp rift that feeds the Eye of Terror will begin to grow, expanding out towards Terra along the Crimson Path, driving a talon of unreality into the Segmentum Solar forevermore and bringing doom to the Imperium. The High Lords of Terra live in constant fear of Abaddon's vision coming to fruition and are sending every military force they can muster to the Cadian Gate as soon as they can get them there. As the drama plays out to its desperate conclusion, just one thing is certain -- there is only war.
- Codex: Chaos Space Marines (6th Edition), pg. 20