With the creation of the Sanctuary

With the creation of the Sanctuary by the angel Inarius and demoness Lilith, the demons and angels who wanted to avoid the Great Conflict between the High Heavens and Pits of the Burning Hells came with them and settled it. The first humans were created as their offspring by mixing the demonic and angelic – the Nephalem. At first they seemed to be nothing like their parent, but quickly it became evident that they wield latent magical powers possibly even greater than their ancestors. Finding this out, Inarius decided to kill them all, but Lilith wanted to make an army to fight the Heaven and Hell. They began fighting, and Lilith, defeated, was banished into the Void – an utterly empty and black space, a prison for various beings – to be eternally trapped there.

Rathma, their son, had avoided the slaughter that followed, and became the servant and student of a mystical dragon-guardian of the Sanctuary – Trag'Oul. After a thousand years, Lilith escaped the Void in the middle of the Sin War events, faming Uldyssian and making him fight the Triune and various related demons with his companions - one of them being Mendeln, his brother. Rathma took in Mendeln, and trained him as his apprentice – the two of them being the first Necromancers, following the teachings of Trag'Oul.

Eventually, Rathma was found and sent to the Void by Inarius, but Trag'Oul sent Mendeln to retrieve Rathma at a great risk. Before the end of the Sin War, Lilith, too, was sent to the Void again, by Inarius. Uldyssian, defeating Inarius, now literally stopped and banished the angels and demons single-handedly – finishing the Sin War. Trying to restore the Sanctuary to it's previous state, he took in all the destruction and damage it suffered during this war, and was guided by Trag'Oul to the Void to release it.

After these events, Rathma and others pleaded with the Heavens and Hells to spare Sanctuary and the humans. Finally a deal was struck to keep Sanctuary and humanity in existance – with no war on either side allowed there.