The Third Galactic Civil War was a galaxy-spanning conflict fought between the Fel Empire and the Galactic Alliance, two of the three founding factions of the Galactic Triumvirate, from 154 to 156 ABY.
While the two factions went to war under the belief that treachery was being plotted by one another, what they didn't know was that the war was actually instigated by the machinations of Darth Nihl's covert Sith remnant. The Jedi Order would later discover this, but by then the Fel Empire and Galactic Alliance were too divided, allowing a full resurgence of the Sith.
Background[]
Since the formation of the Galactic Federation Triumvirate, the three organizations sought the complete unification and prosperity of the galaxy. Instead, tensions systematically began to build as the Empress Marasiah Fel and Admiral Gar Stazi seemed to disagree on nearly every matter of galactic policy. While Jedi Master K'Kruhk would be capable of mediating their council meetings regularly, the time came when even he could not rein in their growing hostility towards one another.
These two would oppose one another so adamently not only due to the differences in their values, but also due to the inner-workings of the One Sith. By 150 ABY, Darth Nihl already had Sith agents in some of the highest offices of government. Some of these agents, hidden within the Council of Moffs and Office of State, used their powers of dark seductions to sew the seeds of paranoia and disconcert into the government.
The Jedi sensed the rising malcontent, but their investigations of potential Sith meddling led them down many dead ends. Tensions continued to rise until 154 ABY, when both Empress Fel and Admiral Stazi were apparently attacked by assassins. Though they survived the assassination attempts, they would accuse one another of perpetrating the attacks using evidence allegedly retrieved from the assassins and go to war; in actuality, neither leader sent assassins but instead, the Sith sent agents against them with the purpose of failing but providing false evidence to lead to hostilities
While the Jedi refused to take up arms for either side in the conflict, they would continue to search for ways to end the war with as little bloodshed as possible and return order to the galaxy. Ultimately, they discovered the role of the Sith in sparking the conflict and though they managed to end the war between the Empire and Alliance with the information, the Triumvirate would remain fragmented for some time afterward.