The Sith Galactic Empire was the second major galactic government from 30 ABY to 50 ABY. Its origins are on the Grand Order, a group of Imperial remnants that united to restore the Galactic Empire. The Grand Order was a faction formed by Imperial groups that survived the Battle of Jakku, such as the 12th Fleet and the Crimson Squadron.
Battle of Jakku
In 5 ABY, the Galactic Empire and the New Republic fought a huge battle on the planet Jakku, located in the Unknown Regions. The Republic defeated the Empire, and it's remnants, although with heavy damage, fled to a planet called Leavantar, deeper within the Unknown Regions.
The Grand Order
After reuniting on Leavantar, the remnants of the Battle of Jakku organized themselves into the Grand Order, and started recruiting people all over the Unknown Regions, including children, for their project, Restoration. As the people from the Unknown Regions were not aware of the atrocities of the Empire, they joined the Order without hesitation. After that, the Grand Order manipulated various events within the New Republic in order to make it weak to the point of a successful invasion, therefore restoring the Galactic Empire.
Joining forces with the Ultimate Sith
In 30 ABY, the Grand Order received a call from a mysterious figure named Darth Kann, who revealed himself to be an apprentice of the former Galactic Emperor Darth Sidious himself. He told the Order that their plans were similar, and told them that they could join forces to restore the Empire, under the condition that it should be ruled by Kann and a Sith Imperial Council. In the beginning, the Grand Order High Command heisted, but later accepted, seeing that fighting Kann would not lead to anything. Then, the Grand Order's Lead Fleet fled to Korriban, meeting up with the Ultimate Sith's Fleet, and Darth Kann sent a transmission to the Galaxy, declaring war on the New Republic and establishing the Sith Galactic Empire, proclaiming himself Emperor and declaring the Jedi enemies of the state again.
Early years (30 ABY - 40 ABY)
New Republic's Fight Hesitation and Fourth Jedi Purge
In the Empire's very first years, the New Republic hesited to fight it, fearing that the Sith would overthrow the Jedi once again and therefore use their power to take over it. It in fact happened, and the Jedi were executed on a plan made by Darth Kann. The Republic was horrified, and the only thing they did was to assemble defense fleets for their most important planets such as Chandrila and Coruscant.
Destruction of Corellia
In 35 ABY, a Maledictus-class Star Destroyer, a Star Destroyer capable of destroying an entire planet, went to Corellia and destroyed the planet, to decrease the New Republic's production of ships and to show them the power of the new Galactic Empire. That awoke the Republic's rage, and they declared open warfare on the Empire.
Late years (40 ABY - 50 ABY)
Battle of Korriban and Dissolvement
In 50 ABY, the New Republic would launch a massive attack on the Empire's capital world Korriban, with the combined forces of all the most powerful fleets in their Navy. The battle took several minutes, almost going up to an hour, when finally the flagship of the Empire was destroyed, which ended up killing Darth Kann.