Kellebos Crusade

The Kellebos Crusade is a castigation Crusade carried out by the Bears of the Claw Space Marine Chapter against the Kellebos System that had fallen afoul of the machinations of the Ruinous Powers, when it was engulfed by a large warp storm, which heralded the uprising of hidden Chaos Cults throughout the system. Overthrowing their Imperial overlords, the cultists then sacrificed thousands of innocent civilians, summoning forth daemonic allies. To make matters worse, a large host of the Word Bearers Traitor Legion invaded the system. The Bears of the Claw were the first Imperial force to answer the call for aid, and soon, a brutal conflict erupted between the Bears and the Heretic Astartes, leaving half the system devastated. Though the Forces of Chaos are eventually driven out of the system, it is a pyrrhic victory at best.

History
When a warp storm engulfs the Kellebos System, the unwary Imperial worlds are subjected to massive insurrections, instigated by long-hidden Chaos Cults secretly aligned with the nefarious Word Bearers Traitor Legion. Through the sacrifice of several thousand innocents, the cultists are able to pierce the veil, summoning a legion of daemonic allies. To make matters worse, a large Chaos fleet arrives in-system - it is the cultists' true masters, the dreaded Word Bearers. The Heretic Astartes launch a planetary assault on the nearest world, and with the successful subjugation of the doomed planet, move onto the next. Slowly, the system is conquered one world at a time. The Bears of the Claw are the first to respond to the desperate calls for aid by the beleaguered worlds of the Kellebos System. The Bears burn a white-hot scar of retribution across the worlds of the Chaos-helf system. The Word Bearers mount a fleet-based crusade of their own, and soon, both sides clash on a hundred battlefields. The war escalates massively as other Adeptus Astartes Chapters join the fight. By the time the system is retaken, the once-populous system has been decimated, with several worlds consumed in nucleonic fire.