Forgotten Aether

16 centuries ago, the powerful and dangerous magical artifact 'Voidbringer' was stolen. The Voidbringer was long believed to be the most dangerous weapon in the multiverse, able to make city-sized spheres of matter completely disappear, and no magic could defend against it. Even deities were subject to it's destructive capabilities.   While the staff has changed hands numerous times throughout it's history, the group that stole it is different from the others. This group managed to develop a method of copying the destructive power of the staff. When the technique inevitably leaked, a cold war arms race sprang up among the numerous powerful factions.   Eventually mounting tensions among the powers lead to a cataclysm of magical war, with every major seat of civilization being attacked and destroyed by Voidbringer copies. However, it turns out people had a fundamental misunderstanding of the Voidbringer's magic. Instead of destroying the subject of it's magic, it instead transported the entirety of it's target to a void plane completely separate from the known multiverse. Millennia of transported bits of matter created a giant black hole that all matter which falls into this plane of existence eventually falls into, at least prior to the great war.   This time, however, the numerous powerful magic users previously at war were forced to band together and create a habitable space in the void. They created a hollow shell of atmosphere, 100 miles thick surrounding the black hole. Their magic was powerful enough to shape the malleable physics of the void plane, and while they cannot escape from the plane, they have created numerous habitable floating cities within the sphere of atmosphere known as the aether.   The armistice that was formed to save the desperate factions from the impending doom of the void has long since shattered, and hostilities have once again resumed.