Star Wars The Rise of Skywalker introduced to us Final Order Sith Eternal Army which was the mightiest army in the whole Galaxy. The Sith Cultists were building a secret Sith Army for 35 years. The Sith Eternal Army consisted of humans only born on Exegol and raised by Sith Cultist in Sith religion. Leader of the Sith Eternal was Dark Lord of the Sith Darth Sidious aka Emperor Palpatine. Despite Sith Eternal Army beeing defeated on Exegol before deploying to free worlds, there are numerous Sith Legions and ships who managed to escape the massacre of Exegol.