Battle of Ygziir

The Battle of Ygziir was the end of the Cremlevian War, a conflict that was waged in the Yuuzhan Vong Galaxy millennia before the Battle of Yavin. One faction of Yuuzhan Vong was led by warmaster Steng, the other by warmaster Yo'gand.

The planet Ygziir was home to a domain (family) loyal to Steng, possibly his home. Presumably it also held either the remainder, or one of the last groups, of Yuuzhan Vong loyal to Steng's faction.

Ygziir was attacked by Yo'gand's forces. Yo'gand used powerful dovin basals (artifical-gravity generators) to pull Ygziir's moon into the planet, destroying both. Also during the battle, he fought Steng, killing him.

Aftermath of the Battle
The Battle of Ygziir was the last conflict of the Cremlevian War. Following the battle, Yo'gand became sole warmaster of the Yuuzhan Vong. Steng's faction gave up resistance, and the race was unified. Yo'gand became the first Supreme Overlord of his people.

The Yuuzhan Vong galaxy had been destroyed over the course of the Cremlevian War. Following its end, and the unification of the Yuuzhan Ving, they decided to leave their galaxy for elsewhere. Yo'gand may have been the one to make this decision.

The tactic of crashing a moon onto its planet later became term the Yo'gand's Core tactic, after its inventor.