The Triumvirate Civil War was a conflict that broke out in 252 ABY after the Galactic Federation Triumvirate fractured between the Dark Empire, a Sith-backed government, and the Alliance of Free Worlds, a Jedi-backed government. The Empire launched it's forces from Wild Space, quickly overrunning the Outer Rim Territories and pushing into the Expansion Region. It was part of a larger series of conflicts known as the New Galactic Wars.
In 251 ABY, Triumvir Johan Fel, one of the three in the Galactic Federation Triumvirate, became the Chief of State. He became obsessed with the Galactic Empire of Palpatine after reading about it in old texts and records. Believing the Empire-in-exile, a semi-autonomous state of the Triumvirate, deserved to lead the galaxy, he made a plot to make himself the new Galactic Emperor. That year, he attempted to commit a coup against the other two Triumvirs on Coruscant. However, Triumvirate Intelligence found out before hand and was able to prevent it, forcing him to flee to the Unknown Regions.
He previously made contact with Darth Mellik, who told him about the return of the One Sith Order. In the Unknown Regions, Fel met with the leader of the Order and negotiated with them: they decided he would become the Emperor. Via hologram he reached out to the Imperial units in the Triumvirate Military, asking them to join him and meet at Kamino, where the Sith were making an army of clone soldiers. There, the final agreements were made and the merging of the One Sith and Empire became a state known as the Dark Empire. Since the Imperials split off, the rest of the Triumvirate was reorganized into the Alliance of Free Worlds. Weeks later, the Empire launched a massive offensive into the Outer Rim Territories.
Course of the War
The War Begins
The Imperial fleets quickly left Wild Space and poured into the Outer Rim, where already many planets declared their willingness to join the Empire. Imperial forces quickly conquered many sectors, in many cases, not meeting any opposition. The Alliance military was not prepared and not adequately positioned for any sort of defense against the Imperial attack. Within months, the majority of the Rim was conquered by the Empire, under command of Admiral Makos Velkor, a Kel Dor officer in the Imperial Navy. He was promoted to Grand Admiral and later Military Executor (commander-in-chief). Other officers that stood out included High General Keyan Harrsk.
There were several major engagements during the Outer Rim offensive, and they were helped by Mel-Pha Renowin, an Imperial Intelligence agent who provided information on the defenses of numerous planets during the campaign, which allowed Imperial forces to overrun them. As the Alliance was pushed back, they began to suffer hardships such as lack of support, as more and more star systems withdrew and either went neutral or joined the Empire. That created a lack of recruits and supplies, which caused the few new enlists to be poorly trained. Meanwhile, the Empire established an organization to create patriots and fanatical followers of the dark side, known as the Commission for Preservation of the Dark Order.
Following the victories in the Outer Rim, in early 253 ABY, the Imperial fleet began quickly overrunning the largely undefended Expansion Region. It was quickly captured, and the Empire began setting up shipyards, factories, and recruitment offices to bleed it dry of resources for the Imperial war effort. As that occurred, Alliance forces were ordered to withdraw to the Inner Rim Territories, where a long blockade was in formation to block the Imperial advance to the Core Worlds. The Imperial fleet swept through the Mid Rim, taking much of it in a matter of weeks. Few Alliance garrisons were left behind to defend it, and they were quickly overrun. The Empire set it's sights on the Inner Rim.
Capture of the Core and Colonies
Agents of Imperial Intelligence discovered the blockade of the Inner Rim, and reported it to Imperial naval command. Several holes were discovered in it, due to the fact that the Alliance did not have the resources to blockade the entire stretch of space. Imperial ships flooded the Inner Rim, preforming a blitzkrieg to destroy much of the Alliance fleet. The entire idea of blockading the Inner Rim was known by historians as one of the most significant factors for the Alliance defeat, as their navy lost the bulk of it's force.