Pit of Raukos
The Pit of Raukos is an ancient warp rift located in an area of realspace that was never claimed by humanity during the Great Crusade. It used to be of no real significance for the galaxy in general: throughout the galaxy there are dozens, if not hundreds of those around, spilling out daemons, Chaos Space Marines and other unpleasant things, and the Pit of Raukos was not a very big or active one.
The Pit of Raukos was, however, a frequent sore in the eyes of the imperial authorities ruling over the territories around the nearby areas, due to the fact that both daemons, chaos marines, and pirates launched raids into the closest imperial worlds. The lack of importance of this area meant that very few resources were dedicated to defend this outposts, so the Chaos forces usually got away with their attacks. However, everything changed with the start of the Cicatrix Maledictum. The general increase of Chaos activity during the expansion of the Great Rift meant that the Pit of Raukos became much more dangerous than usual. Roboute Guilliman and his forces launched an attack to defend the 108/Kapalus-9 system. During that campaign, the Primarch ordered the creation of a Successor Chapter for the Space Wolves, the Wolfspear, comprised of mostly Primaris Marines. Even though the young Wolves wanted to gain the respect of their original chapter, having a warp rift active behind your back is too risky, so Guilliman sent them on guard duty anyways. The young chapter now guards the rift and defends the surrounding area from its chaos activity, and even established their Chapter Monastery on the 108/Kapalus-9 system.