That in Darth Bane: Path of Destruction, Bane causes the very thing that his character revolves around preventing: the extinction of the Sith through infighting.
The Brotherhood of Darkness needed to be purged because they followed Lord Kaan and his asinine beliefs of equality among the Sith. So Bane destroyed them so he could rebuild the Sith Order under The Rule of Two
Don’t try to frieghten me with your EU-worshipping ways, Lord Haseo. Your sad devotion to that ancient canon hasn’t helped you predict VIII or given you clairvoyance enough to predict IX.