Red Scar Campaign
From Warhammer 40k - Lexicanum
The Red Scar Campaign began sometime after the formation of the Great Rift.
The war began when a Tau colonization fleet suddenly appeared due to an empyric convulsion. The Tau immediately began claiming worlds within the Red Scar, the domain of the Blood Angels. The Blood Angels, Flesh Tearers, and Angels Sanguine swiftly led a reconquest of the planets D'sandri and Gendal's Reach before the war spilled into the Sevensuns System.
- 1: Codex: Blood Angels (8th Edition), pg. 22