Ossus Project

Several years after the Yuuzhan Vong War, the Galactic Alliance managed to rebuild itself, although it was fundamentally changed from the pre-invasion New Republic. In 122 ABY, as an effort to strengthen the relationship between the Yuuzhan Vong and the rest of the galaxy, the New Jedi Order authorized Yuuzhan Vong Shapers, under the guidance of Master Shaper Nei Rin, to utilize a remote section of Ossus, one of the most venerable strongholds of the Jedi Order's, as a testing ground.

The intention of project supporters—including Jedi Master Kol Skywalker, a prominent member of the Jedi Council—was to explore whether Vong terraforming techniques, similar to those that had once transformed Coruscant into the species' temporary world of Yuuzhan'tar (27-29 ABY), could revitalize the world that had been left barren and ruined. The experiment seemed to be a resounding success, restoring Ossus to a flourishing state. When the Jedi revealed these results to the wider galaxy, there was an overwhelmingly positive response as other worlds were given an opportunity to restore planets ravaged by the Yuuzhan Vong War.

One hundred planets that had been devastated were chosen as candidates for terraforming. Yuuzhan Vong Shapers, supervised by Jedi escorts, began their work, and the initial outcomes were remarkably impressive, as demonstrated on Wayland.

However, this triumph was short-lived. Operatives from the One Sith, including Sith Lady Darth Maladi and Yuuzhan Vong shaper Zenoc Quah, secretly sabotaged the terraforming processes under the direction of the cult's leader Darth Krayt. Soon, on Wayland, the vegetation of the terraformed world underwent mutations of a kind not seen since the Yuuzhan Vong forcibly took populations as slaves for shaping. Agonizing bony growths erupted from the skin of the natives in a plague that affected all the terraformed worlds, bringing the project to a disastrous conclusion.

The Yuuzhan Vong were deeply disturbed; none of the preliminary trials on Ossus had indicated any of the subsequent mutations. Master Shaper Rin dedicated herself to uncovering what had transpired and why. The Jedi immediately suspected sabotage but were unsure of who was responsible. Many blamed the Yuuzhan Vong, as considerable animosity persisted toward those who had instigated one of the most destructive wars in the galaxy's history. The Sith were aware that the lingering wounds of the Yuuzhan Vong War would lead people to suspect them of such heinous acts. The Jedi, maintaining the innocence of the Yuuzhan Vong, persuaded the Galactic Alliance to support the Yuuzhan Vong against prejudice and unfounded domestic criticism. This angered numerous Alliance worlds, leading many to withdraw from the Galactic Alliance or declare their neutrality.

Meanwhile, the Empire exploited the opportunity created by the loss of confidence in the Galactic Alliance. With the Pellaeon–Gavrisom Treaty that ended its war against the former Rebellion in 19 ABY, the Imperial Remnant had ceased hostilities toward the New Republic as a neutral faction, and the Yuuzhan Vong invasion had united them as allies of the New Republic and its successor. However, its nominal government, the members of the Moff Council, still included many hard-line adherents to the old ways who sought to restore the Empire to its former dominance as the leading galactic power, regardless of the peace treaty. They now called for retribution and, invoking the Treaty of Anaxes, declared war on the Galactic Alliance. The peace that so many had fought and died for in decades past was undone in one swift stroke, all thanks to the resurgent Sith Order.

Anticipating the potential consequences, the Jedi High Council ordered the construction of the Hidden Temple at the onset of hostilities, its location chosen by Nat Skywalker to provide the Jedi with a sanctuary.

From the outset, the Alliance was at a disadvantage. Its defense of the Yuuzhan Vong had alienated many member worlds, whose populations still harbored bitter memories of the Yuuzhan Vong invasion, and many of them refused to support the Alliance. Soon, the Alliance faced not only a widespread war but also a secession movement. The Empire capitalized on this situation, enticing some of these disgruntled worlds into the Imperial camp and weakening the entire Alliance government. Other worlds proclaimed their neutrality. Thus, the war began with the Empire holding all the advantages. However, Emperor Roan Fel himself was less than enthusiastic; he had only reluctantly declared war and never fully committed his support to it. He even forbade his Imperial Knights from participating.

In 128 ABY, one year into the war, the Fel Empire was struggling: despite the Alliance's disadvantage, the Jedi were more than compensating. The Empire lacked the resources to counter the Jedi, and because Fel's Imperial Knights did not participate in the war, the Sith managed to insert themselves into the conflict. Through Nyna Calixte, the ruthless and ambitious Director of Imperial Intelligence and Moff, the Sith approached the Empire and formed an alliance with the Imperial cause. When the Sith revealed themselves, the Jedi realized that they were behind the sabotage of the Yuuzhan Vong terraforming processes, but unfortunately, they were unable to prove it in time to prevent the war. Even members of the Imperial camp—including Emperor Fel himself—recognized the truth, though too late to stop the plans the Sith had set in motion. The Yuuzhan Vong, upon discovering the truth, were initially relieved that their gods were not responsible, and then resolved to undo the damage caused by the sabotage. Shaper Nei Rin traveled from Ossus to try to understand the Siths' method of sabotage, hoping that this knowledge could help discredit the Sith and bring an end to the war.

After three years of intense warfare, the Galactic Alliance was easily conquered, while the Sith grew in power and strength, even independently manufacturing and deploying their own starfighters. Imperial forces had even retaken Coruscant more than a century after the final death of Emperor Palpatine, the Empire's founder and predecessor to Fel and Krayt. The Alliance finally surrendered, and its territories were absorbed into the Empire, with the Galactic Alliance Core Fleet continuing to fight the new Empire. The Emperor called on the Jedi Order to surrender and submit to the Empire; some complied, becoming Imperial Knights. However, the rest, remaining true to the will of the Force, refused to align themselves with the Sith and withdrew from Coruscant to their praxeum on Ossus. The Sith eventually pursued the Jedi there, and Darth Nihl himself led a brutal attack on Ossus, supported by Imperial forces under Moff Rulf Yage. The Massacre at Ossus scattered the Jedi across the Galaxy, although the order was not entirely destroyed. Some Jedi would later return to the planet undetected by Imperial patrols sent to monitor it periodically. Some Yuuzhan Vong, including the Master Shaper in charge of the Project, Nei Rin, also returned to protect any Jedi artifacts that had not been looted by pirates in the aftermath of the Massacre. Cade Skywalker eventually resumed his training on the world under his old Master Wolf Sazen.

Shortly thereafter, the Sith, determined to seize control of the galaxy, launched a revolt to assassinate Emperor Roan Fel and his Imperial Knights. After killing who he later determined to have been a fake, Darth Krayt ascended to the Imperial throne himself, restoring, for the first time in a century and a half since Palpatine, the rule of a Sith Lord over most of the galaxy. Opposition to Krayt's Empire persisted in the form of a rival Imperial faction that remained loyal to Roan Fel and the Galactic Alliance Remnant, which operated from portions of the Alliance that had not yet been subdued.