The Zeist Campaign was a military conflict fought between the Imperium of Man and the Tau Empire, in the Zeist Sector of the Ultima Segmentum. Taking place in 303.999.M41, during the Tau Empire's Third Sphere Expansion, it ran concurrently with Abaddon the Despoiler's 13th Black Crusade and the assault on Imperial space by the Tyranid Hive Fleet Leviathan. As the Imperium's military was heavily involved with preventing the breakout of the Forces of Chaos from the Cadian Gate on the other side of Imperial space, the Tau took advantage of this distraction to rapidly expand their territory. Despite victory belonging to the Imperium, the Zeist Campaign merely allowed the shrewd Tau Commander Shadowsun to rapidly strike deeply into more valuable Imperial space elsewhere. By the time the Zeist C