Bio-Purge of the Octarius System
The Bio-Purge of the Octarius System began in late M41, when the Craftworlds Biel-Tan and Iyanden united to incinerate dozens of Imperium and Ork-held worlds in and around the Octarius System. They achieve this, by using a modified version of the psychic doomsday device used to destroy the world Duriel, which ensured no shred of biomass was left for Hive Fleet Leviathan to consume. This proves to be successful and a large part of the Hive Fleet is isolated and destroyed by interlacing Eldar attacks during the Octarius War. The Imperium however, rages at the Craftworlds' slaughter and blindly attacks any Xenos spaceship within a dozen parsecs of its destroyed worlds.