A Blazing Sunrise
Hundreds of years ago a magical force tore through the world changeing things as it passed. Some areas of the world were left completely untouched while others were changed beyond all recognition. To a much lesser degree the spell plauge is still occuring, occassionaly plucking people from their days for a time before returing them. Where they go no one is certain, even those who have been abducted have no recolection of where they went or how long they were gone. In some exceptionaly rare cases people have dissapeared only to re-appear a generation or more later without aging a day.
Another notable side effect of the spellplauge is that magic worked differently after it passed. Spells that were once the purview of powerful wizards became availible to everyone who had the right training, new spells were born seemingly from nothing, and other spells and items simply stopped functioning all together.
Perhaps the least known change of the spellplauge is that it moved worlds. continents shifted, mountains were created or collapsed, and several planar realms were either moved or ceased to be. Among those planes most heavily affected were both the Nine Hells who were “promoted” to the astral sea and the Abyss who were “demoted” to the primordial chaos.