At the height of their power, they allowed Darth Sidious to rise… Create the Empire and wipe them out.
At the height of their powers, they allowed Darth Sidious to rise create the Empire, and wipe them out.
However, Sidious arrives shortly after to save him and put
him into a suit of black armor that keeps him alive.
At the height of their power, they decided to ascend to Darth Sidious… and create the Empire and eliminate them.
So, despite Ren and Snoke's strong ability in the Dark Side,
they aren't actually the Sith Lords like Vader and Darth Sidious.
The original trilogy begins 19 years later as Vader nears completion of the massive Death
Star space station which will allow him and Sidious, now the Emperor, to crush the rebellion
which has formed against the evil empire.