Realizing that Darth Krayt would not rest until he'd gotten his vengeance against his Empire, Eriaduan Emperor Antonio de Borgia decided that Krayt had to be dealt with once and for all. He joined forces with Cain Knightlord, who was going by the name Contra Mundi, and the deposed Galactic Emperor Roan Fel forming the ruling Triumvirate of the newly formed Galactic Imperium.
Eriaduan Empire divided and reunited
After the defeat of the Empire in the Ascension Wars, the Eriaduan Empire became embroiled in a civil war of sorts. On one hand there was rightful Eriaduan Emperor Borgia, and on the other, Cain Knightlord, Contra Mundi of the Rosen Kreuz Orden. Borgia merely sought sovereignty over the Outer Rim Territories, where as the Contra Mundi wanted dominion over the Galaxy with the Rosenkreuz-controlled Eriaduan Empire at its center.
In 135 ABY, aside from battling Emperor Borgia for supremacy, the Contra Mundi decided to capitalize on the weakness Krayt's Empire was suffering from due to the loss of so many senior Sith and Imperial officials during the war. The Contra Mundi's forces managed to drive Krayt and the remainder of his forces off Coruscant. He then fled to Byss where he remained, quietly, from 135 ABY to 137 ABY.
The Contra Mundi then made quick work of the remainder of the Sith-Imperials near Coruscant and set out to attack Anaxes, administered by a Sith-Imperial governor, in 135 ABY. He laid siege to the fortress world. With the Contra Mundi's forces concentrating on taking down Anaxes, Borgia took advantage and attacked the Contra Mundi from his rear. Caught between Borgia's forces and the Sith-Imperial forces on Anaxes, the Contra Mundi was forced to retreat back to Coruscant. It was around this time that the Contra Mundi formed and alliance with Emperor Fel.
In 137 ABY, once the Contra Mundi and Fel realized that Darth Krayt had assembled an army on Byss and was almost prepared to move against Coruscant, the Contra Mundi, Emperor Fel and Emperor Borgia allied together to get rid of their common foe once and for all. They became known as the Galactic Imperium.
War of the Empires
The triumvirs all agreed that Darth Krayt needed to be eliminated, if history showed them anything it was that the only way to get rid of the Sith is to eradicate them, otherwise they’ll just keep rejuvenating there plans and bolstering their ranks; thus creating an endless cycle, with no clear victor. The combined forces of the triumvirs Emperor Borgia and the Contra Mundi, taking advantage of the fact that Krayt had no knowledge of their alliance, attacked the Sith-Imperial forces on Byss.
After two battles on Byss, the army of the Galactic Imperium was victorious with the defeat of the Sith-Imperial army and the deaths Darth Krayt and his chief lieutenant Darth Wyyrlok (137 ABY). With Darth Krayt's defeat and the triumvir’s control of Coruscant, the Galactic Empire fell into disarray. It was not hard for the forces of the Galactic Imperium to claim dominion over the rest of the Core Worlds and the Inner and Mid Rims. Finally, the Galaxy was once again united under a sole government.
Some time after their victory the triumvirs came to a new agreement on how their new Imperium was to be governed. They decided to divide their territory among the three of them. As the two most powerful in the triumvirate, Borgia took most of the Outer Rim Territories, the Mid Rim Territories, and part of the Expansion Region which while not the most lucrative territory and rife with disorder it put him in a good position for expansion into the Unknown Region, while the Contra Mundi took Coruscant and the rich Core Worlds as well as the Colonies, the Inner Rim Territories, and the remainder of the Expansion Region. Fel, as the weakest of the three leaders, was given control of the eight backwater sectors known as Imperial Space. Henceforth, the contest for supreme power would be between the Contra Mundi and Borgia.
The end of the triumvirate
Borgia and Fel had first to deal with Darth Maladi, the surviving Sith Lord of Darth Krayt's new order, who had taken control of Yaga Minor and was running pirate operations in the whole of the sector, endangering the flow of trade throughout the region. In 143 ABY, Fel, while besieging Maladi's forces on Yaga Minor, ignored Borgia's request that no surrender would be allowed. Borgia then bribed the forces under Fel's command, and they deserted to him. This stripped Fel of all his remaining power as he had no military strength to back it up. It was also around this time that Isaak Fernand von Kämpfer and Dietrich von Lohengrin, two leading members of the Rosen Kreuz Orden, decided that their master should be the sole ruler of the Galactic Imperium, and the Galaxy at large. They started a revolt in Eriadu City, and while they maintained control of the city briefly, Borgia and his forces quickly retook the capital and ousted the Rosenkreuz insurgents. The Contra Mundi was forced to once again reconcile with his fellow triumvir, or rather duumvir at this point.
The Contra Mundi was waging war against the Corellians. His campaign was not as successful as he would have hoped. He took up an amorous relationship with one of his subordinates, Helga von Vogelweide, who gave birth to three children by him. On Eriadu the seized testament of the Contra Mundi (in which he outlined his plans to "remove" Emperor Borgia from his throne) was used by Borgia in a vicious propaganda war accusing the Contra Mundi of treason. He was careful not to attack the Contra Mundi directly, for he was still quite popular in certain circles within the Galactic Imperium; instead, the entire blame was placed on his religious belief and his organization, the Rosen Kreuz Orden.
In 148 ABY war finally broke out. Approximately 200 senators, one-third of the Senate, abandoned Borgia to support the Contra Mundi and Helga. The final confrontation of the Galactic Imperium occurred in 148 ABY, at the Battle of Duro where the fleet of once again-Grand Commander Borgia under the command of Chief Justice Peitros routed the combined Imperium-Rosenkreuz fleet of the Contra Mundi and Helga; the two lovers fled to Coruscant. After his victory, Borgia skillfully used propaganda, negotiation, and bribery to bring the Contra Mundi's forces in the Core, Inner Rim, and Colonies to his side.
Borgia continued towards Coruscant, receiving the submission of local commanders and Rosenkreuz-loyal governors along the way. He finally moved on Coruscant in 149 ABY, but before Borgia could capture him, the Contra Mundi committed suicide. Helga did the same within a few days. The period of civil wars was finally over. Thereafter, there was no one left in the Galaxy who wanted to, or could, stand against Borgia, as the last remaining member of the galactic triumvirate moved to take absolute control.
Dominate power in the Galaxy
He designated governors loyal to him to the half dozen "frontier" systems, where the majority of the military forces were situated, thus, at a stroke, giving him command of enough forces to ensure that no single governor could try to overthrow him. He also reorganized the Senate, purging it of unreliable or dangerous members, and "refilled it" with his supporters, men who could be counted on to follow his lead. However, he left the majority of democratic institutions apparently intact, albeit feeble. It was Borgia who influenced everything and ultimately, controlled the final decisions, and had the armies to back it up, if necessary.
The Imperium Senate and the Imperium citizens, exhausted by lengthy civil wars, were willing to relinquish the rule of the Senate and popular assemblies in favor of a temporary security. By 152 ABY the transition, though subtle and disguised, was made complete. The Galactic Imperium had become the sole ruling body in the Galaxy, and would remain so for almost a thousand years.