The Massacre on Ruusan was a battle of the New Sith Wars.
The Brotherhood of Darkness sent their minions on a diversionary attack on the Jedi forces of General Kiel Charny while the Dark Lords themselves assembled in a meditation circle far away from the battlefield.
There, under the guidance of the recently returned Darth Bane, the Sith joined together to create a wave of Force-powered devastation that decimated the ranks of the Army of Light and scoured the surface of Ruusan.
But before they achieved total victory, Skere Kaan broke from the meditation circle, leading his fellow Lords in a more conventional swoop-based aerial assault on the broken ranks of the Jedi. Although Bane exhorted the departing Sith to reform the circle and complete their task, Kopecz warned him that Kaan and the other Lords had broken away out of fear of Bane's power and ambition that they had sensed through the link.
In the meantime, 300 Jedi Knights under Lord Valenthyne Farfalla had arrived from their confrontation with King Lahzar, fighting through the Sith blockade over Ruusan, arriving just in time to help stave off Kaan's advances. In the ensuing confusion after the battle, the young Padawan Darovit defected to the Sith, but not before killing the heavily wounded and incapacitated Kiel Charny.
Chapter twenty-six of Darth Bane: Path of Destruction established that the six major battles of the Ruusan campaign had already concluded prior to Bane arriving on Ruusan, therefore this battle can not currently be classified as one of the seven battles of Ruusan.
Chapter twenty-six of Darth Bane: Path of Destruction established that the six major battles of the Ruusan campaign had already concluded prior to Bane arriving on Ruusan, therefore this battle can not currently be classified as one of the seven battles of Ruusan.