The First GodsWar

The war between the two factions of Old Gods, or alternatively between the Old Gods and the Demons. The root of the conflict was the debate over whether the newly created lesser races should be immortal (as the faction led by Eyal wanted) or given the Gift of Death (as the faction led by Ema  wanted).
Some of the Dwarves followed their creator Ema, but others joined Eyal's faction.
Most of the Elves followed their creator Eyal, but some rebelled and followed Ema.
After one particularly large battle which ended in a stalemate, Ema and Eyal fought each other in single combat. Ema slew Eyal. Overcome with grief and regret not just for the death of Eyal, but for the division which had come to the Old Gods, Ema withdrew deep beneath the surface of Erdde. There she gave birth to a daughter, Lolth.
With the departure of Ema, new princes emerged to lead the Demon army. Among these were Demogorgon, Orcus, Dagon and Yeenoghu.
The new Demon leaders could not agree on a strategy and their armies fought amongst themselves. Then they were surprised by the Gods' army. In a great battle, many gods, demons, elves, dwarves and other creatures were killed, but the Gods were victorious - at a cost. The Demons were banished to the far places of the world - caves deep underground, the deepest points of the ocean and the hearts of volcanoes - but the Gods lost the power to grant immortality to lesser creatures. Elves and dwarves and other races were doomed to mortality.