With the conclusion of the Great Hyperspace War in 5000 BBY, the victorious Supreme Chancellor Pultimo of the Galactic Republic launched a counterinvasion of the Stygian Caldera aimed at eradicating all traces of the Sith Empire from existence and eliminating any vestigial threat it posed to the safety of the Republic. During this counterinvasion, the reclusive Sith Lord of Nathema, Vitiate, began broadcasting messages of hope to the crumbling remnants of the Empire. Gathering together the last remaining Sith Lords of the old Empire on Nathema with promises of assured victory, Vitiate undertook a a dark-sided ritual that consumed the life essences of the Sith and rendered him functionally immortal.
Naming himself Sith Emperor, Vitiate cobbled together a fleet of Sith personnel carriers laden with young Sith survivors. In 4999 BBY, this fleet of exiles departed Korriban for Dromund Kaas, a forgotten Sith colony recently rediscovered by Vitiate's chief researcher on Nathema. However, in an effort to ensure that the rising generation of Sith were utterly subservient and reliant upon their new Emperor, the Exile fleet wandered aimlessly throughout deep space for the better part of two decades, making hyperspace jumps at random intervals.
Eventually, after this extended perambulation throughout the Unknown Regions, the exile fleet finally came to the forgotten world of Dromund Kaas. Here, amid the jungles and rainforests of that world, the vestigial remnants of the old Sith Empire planned their revenge and return to the galaxy, consolidated into a reconstituted Sith Empire firmly under Vitiate's control. Under the leadership of Odile Vaiken, a Grand Moff who had first served aboard the vessels of the exile fleet as a navigator and pilot, a plan for the implementation of a new Imperial Navy was put into action, leading to the creation of a new Imperial armada over a span of centuries.
- Star Wars: The Old Republic Encyclopedia