Darth Aylen's Sith Empire

Darth Aylen's Sith Empire was a large governing body founded using Sith principles in 289 ABY

Founding
Darth Aylen's Sith Empire was founded mainly due to the power vacuum caused by the Charon War, which had devastated the Galaxy, and weakened the Triumvirate. In 289 ABY, around a month prior to foundation, Darth Aylen had stumbled upon an ancient fleet of Interdictors in almost perfect condition. These ships were taken deep into the Unknown Regions, where they were modified with newer systems, weaponry and shielding. The Fleet then attacked Triumvirate holdings in Wild Space, and captured them with little resistance. The Triumvirate attempted to put up a fight which culminated in the 3rd Battle of Fondor, where they were defeated. Victorious, Darth Aylen pressured the Triumvirate to surrender, which they did, and the resulting Empire would take all of the Triumvirate's northern holdings.

3rd Galactic Civil War
The Third Galactic Civil War was a war that begun in 290 ABY between Darth Aylen's Sith Empire, the Triumvirate, and the Republic of Free Outer Rim Alliances. In the Initial days of the war, the Triumvirate's fleet would be annihilated at the Battle of Kuat and the Battle of Empress Teta. With the capture of Kuat, Darth Aylen would begin to mass manufacture new designs, such as the Interdictor II, a direct successor to the Sith Interdictor. The Triumvirate eventually, with the help of the New Jedi Order, would begin landing heavy blows on the Free Outer Rim Alliances, but they were spread too thin to attack the Sith, who were preparing an Offensive. In the final days of 290 ABY, The Sith would launch a large offensive into the Core Worlds, capturing Coruscant and sending the New Jedi Order into hiding. Without the Jedi's help, the Triumvirate collapsed, leaving the Sith and the Outer Rim Alliances to fight over the scraps. Eventually, by the completion of the Interdictor II fleet, the Outer Rim Alliances would be annihilated. Both were subject to the Sith's terms, and the Sith would take multiple planets, including Kuat and Empress Teta.

Sith Hegemony
Following the Conclusion of the 3rd GCW, there were no galactic powers that rivaled the might and size of the Sith Empire, and as such, they would rule over the Galaxy peacefully for 10 years. Undisturbed, this also marked the construction of one of the largest fleets to date.

Sith-Jedi War
The Jedi would re-emerge in 301 ABY, and rally what was left of Triumvirate and Outer Rim forces against the Sith Empire. The initial campaign was unexpected and dealt a heavy blow. However, success did not last long as the Interdictor II fleet would engage and destroy both fleets. Desperate, the Jedi launched an invasion, targeted at Dromund Kaas. The invasion was a success, the Sith Fleet was largely caught off guard and eliminated. The Jedi would easily sweep through Sith Ground Forces and assault the Citadel, where Darth Aylen was residing. Darth Aylen eventually was forced to confront them, and managed to kill 12 of them before her demise. With her death, the Sith would begin to collapse. However, the High Grand Moff was able to stabilise the empire and launch a counter offensive against the Jedi, resulting in the Great Jedi Purge.

Rebuilding
With the Death of Darth Aylen, the only valid heir, her Daughter, Darth Tylen, would become Empress, and would commission the construction of the Interdictor III Super Star Destroyer, which would be the largest ship in the Sith Empire's Fleet. Eventually, a School of the Dark Arts was opened on Empress Teta, which trained future Sith.