Using the powers of a massive artifact called the Worldstone, they created Sanctuary, a realm hidden from both the Heavens and the Hells.

The demons and angels dwelling on Sanctuary came to mate with each other, spawning powerful hybrids known as nephalem - the first generation of humans. In time, the angels grew fearful of nephalem potential, and tuned the Worldstone to limit their offspring's power. Slowly, over generations, humanity forgot the secrets locked away in its blood.