- "You were deceived. And now, your Republic shall fall."
- —Darth Malgus[src]
The Great Galactic War was a massive, galaxy-wide conflict between the True Sith Empire and the combined forces of the Galactic Republic and the Jedi Order. Other players in the war included the Mandalorians and the Chiss Ascendency, amongst various other minor factions.
The conflict’s origins were in the Great Hyperspace War nearly fifteen hundred years earlier. After the defeat of the Sith Empire at the hands of the Republic, the Sith remnants fled into the Unknown Regions, where they built a new empire under the leadership of the Lord Vitiate, who declared himself Sith Emperor. From their capital of Dromund Kaas, the True Sith Empire built a war machine that would one day return from the shadows and engage the Republic once more.
These plans were discovered by Jedi Knights Revan and Malak, so the Emperor turned them to the dark side of the Force and sent them to test the strength of the Republic in a war. Rather than serving the Emperor, Revan formed a new empire and launched the Jedi Civil War in pursuit of his own power, but he was redeemed and later returned to Dromund Kaas in an effort to stop the Emperor’s plans. Revan was captured and placed into stasis, where his mind was linked with the Emperor’s, allowing Revan to slow the march of war for the next several centuries.
The war was finally launched in 3,681 BBY, when the Sith returned to their ancestral home of Korriban and declared themselves to the Republic. The war went on for decades; countless lives were lost and numerous worlds were devastated across the galaxy, plunging the Republic into chaos and economic depression. Half of the galaxy fell under Sith rule, and the Jedi Order was forced to flee the Core Worlds and seek refuge on their ancestral world of Tython.
By 3,653 BBY, the captive Revan had managed to manipulate the Emperor into pursuing peace. The Republic and the Empire signed the Treaty of Coruscant, after Coruscant itself had been assaulted by the Empire, and the war came to a close. The conflict was not over, however; the galaxy entered into the Cold War, a state of lessened conflict that still saw its share of battles and confrontations, before culminating in the Second Great Galactic War.
- Star Wars: The Old Republic (First appearance)