I'm drunk so bare with me.
Proceeding the events of TFU II's DLC Ending:
Fearing his old age, The Emperor retreated to Byss, where he grew in power for the next six years. Learning to draw in billions inhabitants with the premise of life-long idle luxury, and feed off of their life-Force as they slipped into total apathy. Without any Skywalkers, the Emperor was forced to inhabit a younger clone of himself using a long lost Sith technique known as Essence Transfer. Having outgrown even the likes of Gethzerion and her Nightsisters, The Reborn Emperor seized Dathomir and began conducting experiments, with the aid of the same alchemical scientists who'd aided him in creating his chrysalides on Byss. His plan was to use midi-Chlorians to fertilize the whom of an Nightsister who'd already been corrupted the dark side. The Nightsisters were rich with midi-Chlorians, and those strong enough to become Night Mothers lived unnaturally long lives, and Gethzerion's clan was especially strong with the Force.
The resulting being was far beyond even Anakin in the Force, his infant body overflowed with more than three-hundred thousand midi-Chlorians per cell. The Emperor's essence took the infant's body and mind. When he grew to maturity, his power in the Force was so beyond anything else in the history of the galaxy that his agelessness was assured to him already.
The Emperor used his vast plethora of new super-weapons and Dark Droids from Byss to quickly assume military dominance over any future rebellions and separatist colonies, all Star Systems were made Imperial. It was not long before The Emperor had transformed Coruscant into a second Byss, and afterward most of the systems within the Deep Core would suffer the same fate.
Having reclaimed the galaxy, he knew his rule could not last this time as he continued to tighten his grip. During the battle of Endor the Force had not been with him. He knew that his master had failed in subjugating the Force, because most of the midi-Chlorians his master had attempted to dominate composed beings that were pure of heart.
So The Emperor his Force storms and Force adepts to re-initiate a ritual originally that had originally been prepared by the Ancient Sith Emperor known as Lord Vitiate - albeit but on a slightly smaller scale. The Emperor was careful not to consume the life that he intended to rule over. His ritual seemed to be a success, his presence alone could twist space and distort reality. It seemed that all life could be bent to his will simultaneously, without effort. However, this ritual proved untenable, as the runaway Force storms in fed upon space and time to grow in immensity they left the very fabric of the galaxy...unstable.
His scientists predicted that the outer-galactic belt would be completely dissolved within in a matter of decades. Gathering his remaining Empire, The God Emperor ordered the frantic construction of many Star Worlds, the size of entire solar systems, to preserve his subjects and expand his Empire to other galaxies. The construction of these Star Worlds stripped hundreds of core-worlds of their natural resources, but it was accomplished in time to escape the destruction of the galaxy.
The God Emperor would eventually populate a second galactic community and rule as a God for tens of thousands of years before returning to the Force in a realm of His own design. The God Emperor left behind great works of literature housing secrets of astronomical proportion, endless knowledge that gave immense insight into the power that could be attained through what he considered to be The True Nature of The Force.