Universal Empire

"'We serve only One. One Maker. One Creator. One Destroyer. One Annihilator. One Ruler. One Emperor. One Force. He gives us life. He gives us death. He gives us purpose. He gives us war. With Him, we are strong; without Him, we are dead.' -Incomplete manuscript of the Creed of the Undying, recovered from the Harbringer crash site on Malachor V by spacers in 16 BBY and later translated by Imperial scholars"

The Black Fleet, known for millennia on the original Earth by the Japanese as the Guiding Light of Mitatsu, and only theoretically and posthumously as the Universal Empire, was an ancient Sith cult and military force ruled by Darth Nihilus and, starting in 19 BBY, the beginning stages of an Empire that would have ruled the Universe itself.

History
The Black Fleet was the product of millennia of work and a desire for vengeance against the galaxy, constructed within the asteroid that would be known as Mitatsu by Nihilus.

It was unveiled to the galaxy at large at the climax of the Battle of the Pacific in 19 BBY, and only lasted a year, its threat being prematurely ended by the sacrifice of the young female captain known to history as Hisone Amakasu, and the final death of Nihilus on Malachor V, which resulted in every one of his Sith soldiers collapsing and dying across the galaxy. Had this pivotal event in galactic history been altered drastically, Nihilus and his undead Sith soldiers would've swept through the galaxy and many others, eventually conquering and ruling the known Universe itself.

It is unknown as to what the actual name of the Black Fleet was, or at least, what official name Nihilus had given it. Those few who managed to survive an onslaught of undead warriors of the Dark Side of the Force overhead them referring to it as such, but some theorize that the actual name of the fleet was written in the ancient Sith language in records that are now lost.

Government
Though little is known about what governing body the Black Fleet had, or if it even had a proper government at all, it is generally accepted that Nihilus' servants answered solely to him, so it would seem that it was more akin to a hive mind. Nihilus was its intended emperor, and it is assumed that once he had conquered the known Universe, he would have ruled from a dark throne on Coruscant and would have kept the bare minimum of life alive, accepting a female sacrifice (or as some theorize, several) from any sentient species, once every 74 years. The populace would have been ruled through fear; anyone who had attracted the Dark Lord's ire would have had several Sith soldiers show up at their door and kill them and their families. If an entire world revolted against his rule, it would have likely been dealt with via orbital bombardment, which would have served as a more than sufficient example to the rest of the Universe.

Army
The foot soldiers of the Black Fleet were composed entirely of both stolen droid designs from both the Old Republic and the Reconstituted Sith Empire, and hundreds of quintillions of Force-sensitive clones, the biological descendants of the Force-sensitive children Nihilus had abducted, indoctrinated, and murdered. They carried into battle lightsabers and powerful shieldblasters that could penetrate medium armor, and wore black, hooded armor with red visors that resembled a cross between the Sith troopers of the Reconstitued Sith Empire and those that fought in the New Sith Wars. They were completely loyal to Nihilus, and no attempt to convince any of them to betray him have succeeded; in fact, all attempts to lead them astray have ended in the perpetrators being swiftly struck down by the Sith soldiers. They were as apathetic, sadistic, and cruel as him as well; some would say that they were merely an extension of him and his will, as opposed to individual soldiers. They followed the Creed of the Undying, which was written in the ancient Sith language (many translations of the Creed by scholars in the time of Palpatine's Imperium are incomplete and could be inaccurate) and demanded absolute and unswerving loyalty to him, and worshipped him as the physical embodiment of the Force.

The army also used airspeeder, walker, and tank designs that date back to the 4000s BBY, albeit with many upgrades.

Navy
The navy consisted of untold numbers of augmented Terminus- and Harrower-class warships, new designs such as the Resurgent-class battlecruisers and Mega-class star dreadnoughts, and starfighters which eerily resembled the Mark VI Supremacy-class interceptors; however, they were no longer interceptors, but the perfect combination of space superiority fighter and bomber, much like the Blitz-Falke gunships of the late Reich der Festen Hand.

The navy was originally established and constructed within the ancient shipyards that Nihilus erected in his asteroid, which served as his own realm to rule over in its own right. Originally, the navy was commanded by Sith soldiers deemed skilled enough to operate and maintain large starships. As the Rim Installations were being constructed and more warships were being turned out during the Black Fleet Crisis, however, there was an increasing demand for new recruits, and so Nihilus turned to slave labor for his ever-expanding fleet, just as he did millennia ago.