If SW history has shown us anything, it seems to always go a full circle, the Sith wipe out the Jedi, the Jedi return and wipe out the Sith, the Sith Return and so on, etc etc.
Neither the Sith or Jedi/Republic has had a lasting government.
But yes, the downfall of the Sith is they spend too much time caring about their personal interests and end up fighting with themselves, I think the Sith probably kill more of their forces than the Republic/Jedi.