The First War

The First War was a conflict that occurred before the Material Plane's completion. It was fought among beings of incredible, unparalleled power: gods (usually separated into two groups called Celestials and Prime Evils) and titans. It directly resulted in the near-annihilation of the titans, the separation of the Upper Planes and the Nine Hells, as well as the formation of the Astral Sea-- the "otherspace" between the Outer Planes.