The Vita Merlini, written by Geoffrey of Monmouth tells of the horrifying effect of war trauma on the individual and their families even one as famous and powerful as Merlin. After the Battle of Camlann, Arthur had been taken to Avalon and Britain split into many small kingdoms that fought among themselves. Merlin ruled over the South Welsh giving laws to the people and foretelling the future.
via The Arthurian Realm: The Madness of Merlin — Under the influence!