Dark Angels

Some form of the concept of angel has existed in every culture. The first and most fundamentally associated with the character that would arise from the dark lore were the Seraphim, the burning ones. The other dark order were the Cherubim, the thrones, sphynx like beings, more monstrous than even the Seraphim are described. Where the Seraphim were the deliverers of blessings as well as punishment, the Cherubim were more exclusively punishment.

Describing a real separation between dark angels and light is pointless. It gained popularity as a later convention. I guess people like systems that let them play one power against another. If there is no split, then nothing can offset divine wrath.