The world had been brought into Compliance by the First Legion and Ultramarines, who were led by their Primarch Guilliman. However the First Legion's need to prove their superiority to the Primarch led them to suffer numerous casualties, after they fell into an explosive trap set by the overlords of Karkasarn. The world fell to the two Legions afterwards, but the First Legion angrily left after Guilliman criticized them for their vainglorious victory. The Ultramarines then claimed and set a garrison there, which Artaeon later took command of. However, their were still natives of Karkasarn that refused to accept the Imperium's rule and they unleashed a biogenic phage, that mutated the population. The phage turned the Human population of Karkasarn into blood hungry ghouls, that attacked the Ultramarines. The garrison found themselves heavily outnumbered and sent out a plea for aid, but until they arrived they kept the mutants at bay. Eight months later, the Ultramarines' plea for aid was answered, but to the garrison's surprise it was answered by the Dark Angels. Formally known as the First Legion, the Dark Angels were now led by their Primarch Lion El'Jonson, who quickly deployed his forces and began cutting a swath through the mutant hordes. Seeing this, Artaeon led his surviving Ultramarines to aid them and between the two forces, the mutated population of Karkasarn was destroyed. Afterwards, Artaeon and the Ultramarines expected some rebuke from El'Jonson, due to the last meeting between the two Legions on the world. Perhaps the Primarch would even demand that Karkasarn be given to the Dark Angels to control. El'Jonson, however, had no interest in old grudges and left Karkasarn, after leaving an empty banner to signify the debt to the Ultramarines was paid.