Cahokia

Around 1350 AD of Earth's time, the city of Cahokia was abandoned by the American Indians who had lived there. As Piasa, a dragon, fought excessively and ate people, the beings of the spiritual realm found it to be too dangerous to live on Earth. Thus an angel was chosen to establish and maintain a portal to Realm-R. As part of their task, they were to banish the dragon into Realm-R, and adapt the people of Cahokia to this other dimension in order to keep Piasa sealed. Once in Realm-R, the angel changed the people from their DNA and spirit, turning them into what many Earth inhabitants would classify as Elves. As they were the inhabitants of Cahokia, the angel named their species Cahokia. The people complied, with all the new things about themselves and their purpose, they welcomed the simple name as a reminder of their roots.