23rd century
2256
The Empire during this period in their history was under Philippa Georgiou.
She would continue to fight the rebellion under the Kilgion named Voq. Gerogiou's adviser, Gabriel Lorca of the ISS Buran, and her adopted daughter, Michael Burnham of the ISS Shenzhou, would both plan a coup to overthrow Philippa Burnham, and Lorca were both hunted down and were believed to have been killed.
However, Lorca somehow switched places with its prime counterpart.
The flagship of the fleet at this time was the ISS Charon, which used super-myelical reactor to power the ship.
The reactor, however, pulled power from the Mycelia network, and the usage of the reactor could have destroyed the whole of the multiverse.
During the Empire's attack on the rebels at the planet Harlak, the Charon would be destroyed by the USS Discovery, and Georgiou was taken to the Prime universe and thought to be dead.
She would be later succeeded by her cousin, Lord Alexander.
2267
The Empire was to be considered to be the power of the Alpha and Beta quadrants.
On the ISS Enterprise during this time, there would be a freak transporter accident.
This accident would lead the away teams from both the prime and mirror universes to switch ships.
While in the mirror universe, James T Kirk would speak with the mirror Spock. Kirk would tell Mirror Spock that the Empire could not continue, and the only way was peace.
2268
In a somewhat unprecedented move, Coridan would join the Empire through diplomacy due to the methods of the now Captin Spock.
Spock took the Enterprise from his Kirk through assassination. Spock later rose to the rank of Grand Admiral of Starfleet and Emperor.
During his time as Emperor, he gave the people of the Empire greater freedoms, creating a common forum and a senate; he would also put an end to the operation vanguard as it was a threat to Galatic peace.
He would also end Project Genesis before entering the third phase of planning. This was due to Spock's fear that it would lead to an arms race with the Klingons.
2293
After the destruction of the planet Praxis, the Empire would call for diplomatic talks with the Klingons, Cardassians, and Romulans at Khitomer.
The Tholians did not attend due to tensions between them and the Empire lingering over the Taurus Reach.
The talk, however, ended rather poorly due to no one wanting to form a militaristic alliance with each other.
This action by the Terrans infuriated the Kilingon Regent at the time, Gorkon, who would go on to swear to destroy the Empire.
After the fall of the peace talks, Spock began to prepare a series of reforms for the empire.
However, the people who helped run the empire needed someone to take the blame for the whole mess.
So the Senate would have Spock take the fall for everything wrong that has happened.
Spock would later go into exile and would not be seen or heard from for the better half of a few years.