The Blood War
If ever there was a conflict in the Planes of existence, a conflict that swelled up as if filled with pus, bursting, only to scarrify and atrophy and never heal, only swell up and squirt itself out again, a neverending pus carnival of pain and misery, the Blood War would be that conflict. It raged (and rages still truth be told) between the demons of the Abyss and the fiends of the Nine Hells. Cunning yugoloths may play one side against the other, but the conflict would swell and burst and swell again without much coaxing. It is in both sides' nature to fight.