The Qu'Vat colony was a Klingon outpost, active during the mid-22nd century. The planet hosting the colony had three population centers, one on the northern continent, and two in the southern hemisphere. It's population was estimated by Starfleet to be several million Klingons, mostly in the southern hemisphere.
In 2154, a group of Human Augments led by Malik attempted to deploy biogenic weapons above the colony's southern hemisphere to incite war between the Klingon Empire and Earth. Their attempt was thwarted by Enterprise, resulting in the destruction of the Augments' stolen Bird-of-Prey in orbit of the colony. (ENT: "The Augments")
Unbeknownst the crew of Enterprise, several Augment embryos survived the battle and were retrieved by the Klingon government. Over the next few months, a Klingon scientist named Antaak studied and replicated the altered DNA, creating Klingon Augments and unwittingly unleashing a lethal airborne plague throughout the Empire. To combat the illness, the Klingon government actively sought a cure on Qu'Vat, even kidnapping Denobulan Doctor Phlox and bringing him to the colony.
As a cure was being sought, Klingon Admiral Krell, in league with Earth's Section 31, sent a fleet of warships to destroy the colony and prevent further exposure to the virus. A battle, however, ensued in orbit, between the Klingon vessels and Enterprise and its sister ship, Columbia.