It was in the late 22nd century that the ISS Ranger warped into the Qo'noS system and arrogantly demanded the surrender of the Klingons. The Klingons agreed, and asked only to be allowed to surrender through their own sacred ceremony. Instead, they seized the Ranger and stole its technology, using their slave worlds to fashion copies of the ship.
Emperor Stephane Louvin offered the Klingons a favored role within the empire; however, the legendary Klingon stubbornness and obstinacy prevented them from accepting it and forced the empire to continue the assault. In the end, the Klingons were unable to hold off the Terrans and their allies; nine out of ten Klingon ships were destroyed, and their core colonies smashed. Eventually Imperial Starfleet pushed its way to Qo'noS where General Order 24 was carried out, destroying all life on the planet and turning the Klingons into a race of refugees. With their homeworld conquered, the empire left the few remaining Klingons alone (the Klingons were scattered to the most distant and remote surviving outposts). Now in possession of Qo'noS, the Terran Empire undertook to re-populate the planet using Terran colonists.
Over time, the surviving Klingons focused their efforts on increasing their limited numbers, and striking back at the empire.
Becoming an increasing nuisance, the empire soon determined to exterminate the Klingons beginning in the 2270s and nearly succeeded on several occasions. Nevertheless, the Klingon's struck back with raids deep into the empire's territory, stealing ships and supplies. With the formation of an alliance with the Cardassians, the Klingons were ready to take back their lost homeworld.
In 2293, Qo'noS's moon, Praxis, was blown up in an act of terrorism by the Klingons using Khak'ma bombs. During the resulting chaos on the planet's surface below, Klingon ships massacred the remaining Terran colonists using strafe tactics and reclaimed their homeworld. Upon reoccupying Qo'noS, the Klingons began the process of rebuilding many large cities, including their capital, the First City. The entire planet was remodeled into a dark-majestic fortress world.
By the late-24th century, the mere mention of Qo'noS was enough to strike fear in the many subject-worlds of the Klingon-Cardassian Alliance. Gowron, the Intendant of Qo'noS and its system, ruled over the Klingon people. Moreover, unlike his predocessor, Intendant Worf, Gowron ruled Qo'noS with a combination of cleverness and subtlety. His enemies never knew when he would challenge them to simple combat, use blackmail, or send an assassin to thrust a kut'luch between their ribs. It was also rumored on Qo'noS that Gowron further relied upon the Duras sisters, Lursa and B'Etor, as Enforcers of his will. The appearance of the Duras fleet was enough to sway any planetary system to the Intendant's will. (Decipher RPG module: Through a Glass, Darkly)
No other mirror universe sources mention the Terran Empire conquering and colonizing Qo'noS. It would seem the Through a Glass, Darkly interpretation of events surrounding Mirror Qo'noS is unique.
In 2371, Qo'noS was under threat of destruction from a diamond-shaped Borg ship. After having assimilated an Alliance outpost on Carraya IV, a Borg ship made its way through Alliance territory straight to the Klingon homeworld. Before reaching the planet, the ship exploded in the Kowletz system due to an Iconian computer virus having been uploaded into its systems. (TNG - Mirror Universe novel: The Worst of Both Worlds)