Terran Empire

The Terran Empire was the repressive interstellar government dominated by the $𝜇$ from $𝜇$ in the mirror universe. The Empire ruled by terror, with its $𝜇$ acting as its iron fist. In Starfleet, officers promoted themselves by killing superiors that did not follow the rules of the Empire. Torture was a common form of interrogation. The Empire was the counterpart of the prime universe United Earth and the United Federation of Planets governments. 

Early history
It is not clear when the Empire began. Commander $𝜇$ once stated that the Empire had existed for "centuries" as of 2155. Archer did not mention how many centuries, but by his statement, the Empire can be traced back to at least 1955, suggesting that it was a Terran (Earth) political party or movement before it became an interstellar empire. At some point an astronaut planted the flag of the Terran Empire on Earth's moon, Luna.

First contact
Humanity's first contact with an alien species in the mirror universe began exactly as it did in the traditional universe. Upon detecting $𝜇$'s warp signature, a Vulcan scout ship landed in Bozeman, Montana to make first contact with humanity. Instead of welcoming the Vulcans in a spirit of friendship and understanding, the mirror Zefram Cochrane killed the first Vulcan to set foot on Terran soil, with a gun, as the Humans boarded and ransacked the Vulcan ship after killing the first officer also. According to mirror Archer, the Vulcan first contact was considered a prelude to invasion.

Instead of the Vulcans gradually releasing technology to Earth over time, the Terran Empire applied the stolen Vulcan technology to a policy of aggressive expansion. Because of this, the Empire was able to engage in technological research and development considerably earlier than its United Earth counterpart in the prime universe. For example, Starfleet of the mirror universe had made such inventions as the cloaking device by the mid 22nd century. 

22nd century
Due to the rapid initial expansion made possible by the captured Vulcan technology, The Empire's hold on its territories was initially weak. In the 2150s, some of the worlds conquered by the Terrans were beginning to rebel against Terran rule, leading to a long-running conflict in which the Empire came to the brink of collapse. Propaganda, however, conveyed the message that things were going in the Empire's favor and that the war would be over soon.

By 2155, the Terran Empire had already conquered the Vulcans, Denobulans, Andorians, Aenars, Orions and Tellarites and had launched attacks against the Klingons, Rigelians, and Xindi. However, the flagship of the Empire, the Enterprise, under the command of Captain Maximilian Forrest, had a much more racially-diverse crew than its regular universe counterpart, with numerous Vulcans and Tellarites serving as crewmembers.

In that year, the USS Defiant (NCC-1764), a Federation ship launched in the 23rd century of a parallel universe, was reported in Tholian space. The first officer of the ISS Enterprise, Commander $𝜇$, reviewed the reception of this distress call and proposed a bold surgical strike at the asteroid base at which the Tholians were keeping the Defiant. Archer's proposal was quickly rejected by Forrest, causing Archer to mutiny against his Captain and take control of Enterprise to retrieve the Defiant so its technology could be utilized against the rebellion. Enterprise arrived and dispatched a boarding party to gain all information they could about the ship, and destroy it to prevent the Tholians from being able to use it. Unfortunately, during the retrieval operation, the Tholians attacked Enterprise and destroyed it, stranding the boarding party aboard the Defiant. 

Following the destruction of the ISS Enterprise and the death of Captain Forrest, Commander Archer and his away team commandeered the USS Defiant. They proceeded to destroy the Tholian hangar in which the ship was being held and rescued a number of former Enterprise crewmembers, including $𝜇$, after apparent consideration of leaving their comrades stranded. Archer made a rendezvous with the, the flagship of Admiral Black. Archer vaporized the admiral and took command of both vessels. Commander $𝜇$ and Crewman $𝜇$ led a mutiny of the non-Human crewmembers on board the Avenger and attacked the Defiant in hopes of destroying it. They were destroyed after Commander $𝜇$ reinitialized the power systems that $𝜇$ had attempted to disable. Commander Archer, acting as Captain, then set a direct course for Earth, where he intended to declare himself Emperor of the Terran Empire. However, Hoshi Sato poisoned him with the assistance of his bodyguard $𝜇$. The two then took control of the Defiant, and upon arriving at Earth, Sato declared herself Empress. 

Somewhere between 2155 and 2267, the symbol of the Empire appears to have been altered. The earlier symbol closely resembles that of the United Earth government, depicting all of Earth's continents, though replacing a laurel of peace with an aggressive sword. However, by the mid-23rd century, the symbol, while remaining essentially the same, depicted only the continents of Earth's western hemisphere, suggesting the seeds of the Empire were sown in that hemisphere.

23rd and 24th centuries
In 2267, crewmembers of the USS Enterprise (NCC-1701), including Captain James T. Kirk, were accidentally transported to the mirror universe aboard the mirror-version of the Enterprise, the. Before Kirk left, believing that the mirror $𝜇$ would one day become captain of the ISS Enterprise, he planted a seed of doubt about the inevitability of the Empire, asking Spock if violence was the only logical answer. Spock promised to consider Kirk's words, after realizing the Empire would only last about 240 years before being overthrown. 

As Kirk predicted, the mirror-Spock later became the captain of the ISS Enterprise and eventually rose to become Commander-in-Chief of the Empire. He began instituting major reforms that were very popular, turning the Empire into a more peaceful and less aggressive power. Unfortunately, Spock's reforms left the Empire unprepared to defend itself against the emerging threat of a united Klingon-Cardassian Alliance, which managed to conquer the entire Terran Empire, turning the Terrans themselves into a slave race. The Bajorans, a people conquered by the Empire, came to be a powerful voice in this Alliance. 

Subjugated Races

 * Andorians
 * Denobulans
 * Orions
 * Tellarites
 * Vulcans
 * Bajorans
 * Halkans

Apocrypha
In Star Trek Online, by 2409 the Terran Rebellion has succeeded in overthrowing the Klingon-Cardassian Alliance and restored the Terran Empire to its former status as a major power in the quadrant. The Empire - led by Captain James O'Brien - has also returned to the old ways, and attempts to invade the prime universe using a trans-dimensional portal in the Arawath system. Imperial ships have markings similar to those used in the 22nd century.

In the game Star Trek: Voyager - Elite Force, part of the story involves going through a scavenger base composed of many species' ships. One of these ships is a Empire Starfleet vessel, apparently dating back to the 23rd Century. It is populated by Humans, who behave typically for the mirror universe. How it came to be in Voyager's canon dimension is unknown.