1197, Ancient Troll
This Sith civil war had been absurd, but by sheer coincidence, it had produced an excellent outcome.
When the Jedi Order remembered Planet Korriban once more and sent people to investigate, they found a devastated Korriban in the aftermath of the Sith civil war. Just as they had expected, it was a barren wasteland.
Little did they know that the Sith had actually been putting down roots and flourishing on Planet Korriban all along. They had grown powerful enough to fight a civil war, then wiped themselves out in the process.
This gave the Galactic Republic and the Jedi Order a terribly mistaken impression—they believed the Sith Order had indeed been destroyed, with no sign whatsoever of rebuilding. Thus, although they stationed a fleet on Planet Korriban for the long term, their guard was extremely lax.
The result was that when the reformed and rebuilt New Sith Empire gradually rose to power over the following thousand years, restored its military might, and retook Planet Korriban, the Republic fleet stationed here was utterly defeated.
After reclaiming Planet Korriban, the New Sith Empire rebuilt the Sith Academy, and this place once again became the center of Dark Side Force.
However, the Eternal Empire suddenly appeared at that time and intervened in the war between the Galactic Republic and the New Sith Empire. During this three-way conflict, Planet Korriban was destroyed once again by the Eternal Empire fleet, and countless Sith Temples were buried beneath endless yellow sands.
After that, with the Eternal Empire's defeat and the fall of the New Sith Empire, Planet Korriban never regained its former glory. It merely became a silent, dead planet, forgotten by all.
In truth, as a holy land of the Dark Side, Planet Korriban had drawn many Sith Lords throughout the ages.