The Seventh Battle of Ruusan

The Seventh Battle of Ruusan was the final major engagement of the conflict known as the New Sith Wars. There were actually seven prior battles on the world during the last days of the war, but the pivotal and last battle is the one most remembered, due to the use of the thought bomb; it is usually referred to just as the Battle of Ruusan. This was also the event that would lead to the Ruusan Reformation of the Galactic Republic.

"I ask that you join me in one last task: the creation of a weapon so powerful that when it is detonated, the victors shall become the vanquished and be swept from the pages of history."
―Kaan
The New Sith Wars began 2,000 years before the Battle of Yavin and ended after a thousand years of conflict, including internal Sith conflict, and all-out assaults on the Galactic Republic. At one stage during the long war, the Sith had been in control of most of the galaxy, but the Army of Light slowly regained the Republic's lost territory with decades of hard-fought campaigns.

Eventually, the Sith retreated to Ruusan, where, after six months of battle with the Jedi in six separate battles, the Sith were near defeat.

The Jedi Lord Valenthyne Farfalla crushed the Sith in the pivotal seventh battle of Ruusan, and Lord Hoth journeyed to apprehend the leaders of the Brotherhood of Darkness. The Sith, however, were waiting for them and had one final weapon.

"What is this?"
"Kaan's smartest decision—his suicide."
―Zannah and Darth Bane.
In an act of desperation, Lord Kaan, leader of the Sith, unleashed the thought bomb and in an instant, every Force-sensitive in the blast radius was destroyed. Lord Farfalla had retreated with the majority of the Army of Light in accordance with Lord Hoth's final orders. The only surviving Sith was Darth Bane, who, while leaving the battlefield, came across the young girl Zannah.