Endless ages ago, the first devils began their interplanar travels, greedily attempting to occupy everything. They traversed the Cassery Plane and eventually arrived at the Abyss.
It was here that they first encountered the Tanari Demons.
Order Evil and Chaotic Evil, two fiend races with inherently conflicting ideas, inevitably clashed, manifested in hateful slaughter.
Soon, these devils were almost entirely wiped out, but a small group managed to escape back to Barto Hell to report their findings, and both sides became aware of the other's existence.
Initially, the conflicts were skirmishes involving small contingents; however, these encounters quickly escalated into local wars, which then evolved into full-scale war. Thus began the most brutal and enduring war in the multiverse—the Blood War.