Carthodox was a militarized religion monotheistic and procreative, they came into conflict with the necromongers during the Fourth Regime.
The Necromongers and Carthordox came into conflict during the fourth regime of the Necromongers, under the Lord Marshal Baylock the Brutal. The two religions crossing paths while trying to convert the worlds of the Neibaum system, the worlds becoming a holy battlefield.
An interesting though probably irrelevant footnote to the history of this particular conflict: there are suggestions, oral history only, that the Elemental race was advising the Carthodox in the course of this war. But many doubt this, citing the traditional neutrality of all Elementals.