ARNOR / DREAD LORDS

Planet of Origin: Amalda in the Amaldia system
The Arnor were a powerful civilization that existed millions of years ago and which got politically divided in two factions, one calling themselves Arnor, the other one, Dread Lords. As the Dread Lords were on the brink of conquering the galaxy, the Arnor , on the brink of extinction, sealed them away into a pocket universe. It remains unknown what happened to them afterward.
Source: Galactic Civilizations

ALTARIANS / DRATH

Planet of Origin: Altaria, a planet orbiting Altaris. Relocated to Dratha in the Drathis system after a war with the altarians.
The Drath Legion is a reptilian civilization that was nearly wiped out by their homeworld's other more numerous sentient species, the Altarians during a dominance war and who consider themselves the true Altarians. The Drath are passive-aggressive manipulators, remaining hidden and pulling the strings on the weak and powerful alike with subtlety in mind and seemingly infinite patience.
Source: Galactic Civilizations