The Blood War is a cosmic conflict in the Planescape setting of the Dungeons & Dragons universe. It primarily involves the forces of Lawful Evil and Chaotic Evil, specifically the devils of Baator and the demons of the Abyss. This war is fought over the souls of mortals and the control of the multiverse, with each side seeking to gain dominance over the other. The Blood War has significant implications for the Outer Planes, influencing the politics and power dynamics among various factions and creatures. It also affects the modrons, inevitables, and other beings that may be drawn into the conflict, as the war creates ripples throughout the multiverse.