The Ethnarchy was a powerful faction which existed on Terra towards the end of the Unification Wars. Ruled over by Eugenicist oligarchs, they maintained a small empire over the Caucasus which was protected by formidable Power Field generators. The Ethnarchy is known to have commanded formidable forces consisting of genetically modified warriors known as the Ur-Khasis, dangerous weapons from the Dark Age of Technology, and enslaved Psykers. The first attempt by Imperial forces to capture the Ethnarchy's strongholds earlier in the war had cost the lives of 20,000 Legiones Astartes and a million other casualties.
Towards the end of the Unification Wars, the Emperor began his second attempt to topple the Ethnarchy. This time the XVIII Legion (later known as the Salamanders) was tasked with destroying the subterranean power generators feeding the Ethnarchy's power fields. In the ensuing Assault on the Tempest Galleries, the XVIIIth Legion was victorious and with their force fields down, the Ethnarchy was quickly crushed by the forces of the Emperor.