Blood Wars (Dungeons & Dragons)

It is set in Dungeons & Dragons.

The Blood War was an ancient conflict that raged between the fiends of the Lower planes.

The two main sides of the war were the demons (Chaotic Evil), inhabitants of the evil plane of chaos of the Abyss; and devils (Legal Evil), representing the equally evil but lawful realm of the Nine Hells. Neutral evil yugoloths played both sides against one another.

The Blood War had raged on since the Age Before Ages, a dark time when the Prime Material Plane had not fully developed. The conflict was massive, spanning entire planes of reality and hosting an almost infinite number of fiends.

The higher planes (Good and Neutral) always support the side that is at risk of losing, sending men, weapons and personnel. They know that if one side loses, the winner will be an unstoppable force. Demons are a particularly feared force due to their sheer numbers and brute force.