Gerrhae War

The Gerrhae War was a campaign fought against the vile Tzeentchian warband known as the Host of the Unending Tower by the Ordinators Space Marine Chapter and allies from the Inquisition's Ordo Malleus.

History
A Tzeentchian Warband, the Host of the Unending Tower, ambushes and massacres an Ordinator frigate carrying a fell tome of dark knowledge through an artificial warp rift, seizing it and using its knowledge to begin carving out a realm of its own in the Gerrhae Sector within the Segmentum Pacificus. The Ordinators, along with an allied chapter, eventually turn the tide with the help of the Ordo Malleus by sealing the warp rift and either liberating or exterminating any planet along the path of the Cult - led by the dual Sorcerer-Kings of Land and Void, Nagem and Ahtu, respectively. Though the war is incredibly costly and results in the destruction of the sector's de facto capital of Bellator - it comes to a decisive end with the deaths of Ahtu in the Battle of of the Blood Nebula, followed by the slaying of Nagem's entire Chaos Space Marine warband as well as their patron Lord of Change, O'kazhk's banishment, above and upon the surface of the the newly re-inhabited world of Martyr's Hope.