Umbral Humans

During the Great Expansion some tribes of Humans were seeking to exterminate the Shadar-Kai Kingdom, which ruled a strip of land nowadays split between Abendland and Nordenland. as the Shadar-Kai fled into the Shadowfell, armies of men followed. A ritual of the Elves closed the local portal between realms and shut both folks off from the material realm.
The exposure to shadow corruption transformed humans to so called Umbral Humans as they conquered a part of Edorchadas and declared the Umbral Empire. They are still at war with the Shadar-Kai which integrated into Shadow Fey society.