The Mad Inquisitor and the Traitor Marines
Some five hundred years ago, Livia Zilliacus, Inquisitor of the Ordo Hereticus, was struck by the revelation that the holy intentions of the True God-Emperor had been twisted by the the Imperium’s new leadership. While this drove her utterly mad, it also drove her into action. She declared the entire Echlesiarchy heretical and in the name of the True Emperor declared war on all of the Imperium.
The Mad Inquisitor was not alone on her traitorous crusade, however. She managed to persuade an influential Chaplain of the Space Marines of her views, and together they turned the entire Chapter to their cause.
The Chapter renamed itself the Argent Crusade and took silver, black and blue as its primary colors.
The Early Crusade and the Loss of the Homeworld
After a few initial foolhardy attacks on Imperium forces, Ferrosa, the Argent Crusade Homeworld was attacked and completely destroyed by a combination of Ultramarine, Imperial Fist and Raven Guard forces. A large part of the Argent Crusade was lost in the failed defense of the Fortress-Monastery and the surviving forces fled Imperial Space to consolidate and rebuild its strength.
Remobilizing the Crusade
Without a Homeworld, and having lost two thirds of their forces, the Argent Crusade spent a long time rebuilding. They raided worlds on the border of Imperium space for resources using hit-and-run tactics, and clashed with Imperial forces on several occasions.
The Crusade has now established control over a number of systems outside Imperial space and are building a regular army to complement the Astartes. Two worlds, Kerry and Sstarx, have even turned out to provide warriors with enough potential to start recruiting new Initiates, and slowly the Crusade's ranks of Astartes are beginning to grow again.