On Manaan, after over a decade of occupation, the Galactic Empire had become careless with its garrison in Ahto City. Shortly before troop rotation, Darth Vader arrived on the world and met with the members of the Order of Shasa. Believing him to be a Jedi, the Shasans listened to him as he gave them details on the troop movements, as well as his plan on how to beat them.
Bolstered by his dark side abilities, two hundred Shasans swam through the sewers of Ahto City, surprising and killing many of the inexperienced guards. The remainder of the Imperial garrison evacuated the planet. The Shasans planned to let the tourists of Ahto Luxury Resorts leave unharmed, but after again being immersed in the dark side, massacred them all.
Vader later met with the Order, informed them of the demise of the Jedi Order, and told them that they now served his own master.
Fewash Welko later recounted the battle in his book, The Battle of Ahto: A Memoir.