The period of the
sith history know as The Golden Age of the Sith preceeds by many millenia the events described in the
Star Wars movies and even the events told in the Tales of the Jedi
comics.
This period followed the exile of the dark jedis that eventually became the Gods and Lords of the sith and was a time for expasion for the sith, once a primitive race, now forced by evil jedi to fight and conquest for then. The military strength of the Sith Empire in this age was a match for that of the Republic. If not for internal Civil War, the siths would had won The Great Hyperspace War.