The Cremlevian War, a struggle fought within the Yuuzhan Vong galaxy thousands of years prior to the Battle of Yavin, concluded with the Battle of Ygziir. Warmaster Steng commanded one side of the Yuuzhan Vong in this conflict, while the other was under the leadership of warmaster Yo'gand.
Ygziir, a world that housed a domain faithful to Steng, became the target of Yo'gand's assault. Employing potent dovin basals, Yo'gand manipulated Ygziir's moon, drawing it into a collision course with the planet, resulting in mutual annihilation. During the fierce battle, Yo'gand engaged Steng in direct combat, ultimately ending his life. The Battle of Ygziir marked the cessation of the Cremlevian War. In the aftermath of this battle, Yo'gand ascended to the position of sole warmaster of the Yuuzhan Vong. Steng's faction either surrendered or was completely eradicated, leading to the unification of the race under Yo'gand, who became the first Supreme Overlord of the Yuuzhan Vong. The Cremlevian War had ravaged the Yuuzhan Vong galaxy. After the war's conclusion and the Yuuzhan Vong's unification, Yo'gand made the decision to seek a new home beyond their destroyed galaxy. Furthermore, the strategy of using a moon as a planetary weapon was later designated as the Yo'gand's Core maneuver, in honor of its originator.