Originally posted by roughrider
You know the history expanded upon in the Phantom Menace novelization - it was the great number of Sith users a thousand years earlier, that help seal their fate against the Jedi. They fought & killed amongst themselves, because the dark side makes you greedy for power, so they helped the Jedi in wiping themselves out. The surviving Sith made a pledge to always keep their numbers small after that.
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Unfortently the EU made this mythical Sith, Darth Bane, into a joke/fanboy's wet dream. Disapointing really, considering how cool the story sounded in the novel.