The Tallanar Sector is on the western edge of Imperial Space, for the most part it is isolated from the rest of the Imperium. the Tallanar Sector only has three inhabbited planets:
Tallanar: a post nuclear age civilized world
Sovereign's Refuge: a hive world
Altos IV: a feral death world that is also home of the Doom Crusaders' Fortress-Monastery. the Citizens od Altos IV have develpoed a clan oriented caste system which has carried over to the Doom Crusaders.
All contact was lost with the sector when it was swallowed by warp storms after the Great Heresy. in the 39th Millenia an Imperial Fist fleet were chasing a group of Eldar Pirates, when they stumbled onto Altos Iv under attack from Orks, the Imperial Fists temporally stoped chasing the Dark Eldar and forced the Orks off the planet. Captain Rico, of the Imperial Fists reccomended a Space Marine chapter to be created using the Tallanar Sector as a base, the Administratum agrred and the Doom Crusaders were founded and built thier fortress monastery on Altos IV. Today the Doom Crusader are busy fighting the Orks that continue to attempt to capture the Tallanar Sector.