The Thramas Crusade was a protracted campaign of the Horus Heresy fought in the Thramas sector, a war of shadows and attrition between two of the most enigmatic primarchs and their Legions. It pitted the Dark Angels, led by Lion El'Jonson, against the Night Lords under the tormented Konrad Curze, in a struggle Horus intended to keep both distracted from the wider rebellion.
The Dark Angels had been dispatched to hold the region and hunt down the traitor Night Lords, whose master had embraced terror and cruelty as instruments of war. What followed was a grinding void campaign of raids, ambushes, and reprisals, as the two forces stalked one another across the sector's worlds and shipping lanes. Curze's warriors excelled at fear and misdirection, drawing out the conflict and denying the Lion a swift victory.
The crusade grew intensely personal, culminating in brutal confrontations between the two primarchs themselves, each the other's equal in ferocity and guile. Though the Dark Angels eventually gained the upper hand and shattered the Night Lords' fleet, Curze survived to slink away, his Legion scattered but unbroken in spirit. The campaign had achieved Horus's aim of pinning down a powerful loyalist force, and it forged a bitter enmity between the two Legions that would echo through the remainder of the great betrayal.