system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] "Once more the Sith will rule the galaxy" - Palpatine: When did the Sith rule the galaxy, and what all do we know of this time period?
gpt
In Legends and in canon, there had been multipl massive Sith Empires millennia in the past.

Their final defeat in Legends came after the Battle of Ruusan, a thousand years prior to Palpatine's rise as Chancellor then Emperor.

In canon, something similar happened,  but we don't know where they were finally defeated; we only know the sole survivor, Darth Bane, created a new Sith Order, based on the Rule of Two (one master, one apprentice, no more Sith beyond that) that ended with the deaths of Palpatine and Darth Vader.