The Cremlevian War represented an internal conflict among the Yuuzhan Vong species. This war, a clash between a domain under the leadership of Warmaster Yo'gand and another domain commanded by Warmaster Steng, resulted in widespread devastation across the Yuuzhan Vong's original home galaxy. Ultimately, Yo'gand's domain emerged victorious following the Battle of Ygziir circa 15,000 BBY. Nevertheless, the galaxy was left in a state of ruin, and the bellicose Yuuzhan Vong were stripped of their connection to the Force by the sentient planet known as Yuuzhan'tar. Consequently, the Yuuzhan Vong abandoned their ravaged galaxy, venturing into the Intergalactic Void in search of a new place to settle.
The Yuuzhan Vong's world, Yuuzhan'tar.
The genesis of the Cremlevian War can be traced back to an invasion launched by a droid species within the Yuuzhan Vong's galaxy. Facing potential annihilation, the Yuuzhan Vong innovated, creating novel weaponry and technology, ultimately securing victory against their droid adversaries. Following this triumph, the Yuuzhan Vong persisted in their warfare against other species inhabiting the galaxy, successfully conquering numerous worlds. However, internal strife began to plague the species.
Eventually, the two most dominant factions—one under the command of Warmaster Yo'gand and another led by Warmaster Steng—engaged in conflict. The resulting Cremlevian War led to the destruction of countless planets. The war reached its conclusion around 15,000 BBY, when Yo'gand employed a technique that would later bear his name, causing a moon to collide with the planet Ygziir, an ally of Steng. This tactic obliterated the planet and killed many of Steng's faction leaders who were stationed on Ygziir. Steng's death in the battle also marked the end of the war.
Yo'gand ascended to the position of the Yuuzhan Vong's first Supreme Overlord, unifying the species under his rule. He was celebrated as a hero for his deeds, and the Battle of Ygziir was revered as the most glorious moment in Yuuzhan Vong history. However, the Cremlevian War left the Yuuzhan Vong's galaxy in ruins. Many planets were either destroyed or severely damaged during the conflict; the Yuuzhan Vong's sentient homeworld, Yuuzhan'tar, was among those that suffered. The war had instilled a thirst for violence in the Yuuzhan Vong, and Yuuzhan'tar severed the bloodthirsty species' connection to the Force. The Yuuzhan Vong then embraced the worship of pain and adopted a philosophy centered on violence and death for all who opposed them. After millennia of ferocity and destruction, the galaxy was depleted of its resources and lay in ruin. The Yuuzhan Vong abandoned their galaxy to roam the Intergalactic Void. Eventually, they discovered a new galaxy, which they invaded with the intention of conquering it.
The Cremlevian War was initially referenced in The New Jedi Order: Vector Prime, the inaugural novel of The New Jedi Order series. Subsequent mentions appeared in The New Jedi Order: Destiny's Way, The New Jedi Order: The Unifying Force, and various reference guides that provided further details regarding this ancient conflict. It also received an entry in The Complete Star Wars Encyclopedia.
According to author Daniel Wallace's blog, The New Essential Guide to Droids suggests that the Silentium and the Abominor were the droid species responsible for invading the Yuuzhan Vong and threatening to wipe them out. However, this remains speculative, as it has not been officially confirmed.