The Nulvarl Empire was the name for the group of planets that was founded by Dark Jedi Mastal and his two apprentices, Jorell and Trivas. After overthrowing their master, the apprentices reigned there for several years until the Areltsi War resulted in Trivas being exiled.
Many years later, Jorell had conquered more systems and decided to attack the Sith. The empire was conquered by the Sith and Chiss Ascendancy as result of these actions. The Chiss, mostly due to Syndic Fel's advice, gave up claim on the conquered planets. Trivas took possession of the Nulvarl Empire and renamed it the Nymean Ascendancy.