The New Republic suffered a defeat at the Battle of Duro during the Yuuzhan Vong War. Duro, a world within the Core, became the first to fall under the control of the Yuuzhan Vong. The New Republic's original intention was to rehabilitate this polluted planet and provide a home for millions of refugees who had been displaced.
During the conflict, the Yuuzhan Vong employed Dovin basals, devices that caused the floating cities to plummet to the planet's surface. Except for Urrdorf City, which successfully escaped with thousands of Duros, all of these cities were obliterated upon impact. Furthermore, the Yuuzhan Vong unleashed the Ychna, a colossal space serpent that targeted the orbital city of Orr-Om, alongside two formidable serpentine monsters named Tu-Scart and Sgauru. Nevertheless, Jedi Knight Anakin Solo managed to destroy the Ychna by launching a proton torpedo into its open mouth. Despite this victory, the Yuuzhan Vong were successful in their conquest of Duro.
In the course of the battle, Leia Organa Solo was captured by Warmaster Tsavong Lah, who subjected her to torture nearly to the point of paralysis. Lah's intention was to offer Leia as a sacrifice to Yun-Yammka, the God of War and the primary deity of the Warrior caste. Jacen Solo, Leia's son, located his mother, but Lah remained confident, having heard of Jacen's pacifistic nature. Jacen had been attempting to disconnect himself from the Force to avoid participating in violence, but he now faced the choice of using the Force or allowing his mother to die. Ultimately, Jacen acted instinctively. He utilized the Force to create a whirlwind of surrounding objects, which he then used to knock Lah out of a window, severing the Warmaster's left foot in the process.
Following his defeat, Lah proposed a cessation of the invasion at Duro, promising to leave the remainder of the galaxy undisturbed. However, in exchange, Tsavong Lah, a staunch opponent of the Jedi, demanded the deaths of all Jedi. Any planet offering refuge to a Jedi would become a target for attack. Most of the galaxy incorrectly identified non-Jedi Force-sensitives as Jedi and included them in the demand.
Nas Choka, who eventually succeeded Lah as Warmaster, was critical of this decision from the beginning, arguing that Lah devoted too many resources to eliminating the Jedi. Nevertheless, many planets took Lah's words seriously. Several Jedi Knights were either killed or betrayed to the Yuuzhan Vong in the hope of gaining protection or favorable treatment.