This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
The Federation-Klingon War was a conflict fought between the United Federation of Planets and the Klingon Empire that began in 2256 with the Battle of the Binary Stars on stardate 1207.3. This battle was provoked by T'Kuvma, a Klingon from the House of T'Kuvma, to rally the Empire to a common cause as he had portrayed the Federation as an existential threat, whose space had encroached unacceptably close upon that of the Klingons. In the first six months, the Federation lost 8,186 people. (DIS: "Battle at the Binary Stars", "Context Is for Kings")
Captain Gabriel Lorca of the USS Discovery claimed that sometime after the war began, he was given the freedom to do whatever it took to win the war, even if it meant breaking the rules of Starfleet. As part of this effort, Starfleet co-opted the research by Paul Stamets and Straal into an experimental spore drive. Six months into the war, the Discovery managed to practically implement the drive and went on to achieve a string of victories. This was made possible by capturing an alien it called a Tardigrade. (DIS: "Context Is for Kings", "Choose Your Pain")
In November 2256, a Klingon force managed to slip past the blockade defending Corvan II, a major resource hub whose mines produced forty percent of the dilithium supplies in the Federation. Without the planetoid, a sizable part of Starfleet would be grounded. By the time the colony managed to get out a distress call, the planetary defense shields would only hold another six hours under the continued Klingon bombardment. With the closest ship much further away, the Discovery quickly responded, outmaneuvered, and destroyed the attacking Klingon vessels using its experimental spore drive. (DIS: "The Butcher's Knife Cares Not for the Lamb's Cry")
After their first success with the spore drive, Discovery quickly became the most important weapon in the Federation arsenal, causing the tide to turn and the Federation to start winning. In the three weeks following the relief of Corvan II, Discovery further used its drive to break the Klingon supply line at Benzar and rout an attack through the Ophiucus system. Starfleet started building spore drive units in a secret facility on Earth, while directing every ship, colony and starbase to search for more Tardigrades. (DIS: "Choose Your Pain", "Magic to Make the Sanest Man Go Mad")
Around this time, General Kol established a new ruling council. Starfleet believed that he had ousted the House of D'Ghor and the House of Mo'Kai, who secretly approached Vulcan to discuss a potential alliance. However, this was in fact a ruse by Kol to capture a high-ranking Vulcan. The plan worked better than expected when, due to unforeseen circumstances, Admiral Katrina Cornwell arrived in the place of Sarek. After Cornwell's capture, Kol welcomed Dennas' and Ujilli's Houses into his empire and promised them cloaking technology. (DIS: "Lethe")
As more houses joined General Kol, the number of ships utilizing cloaking technology increased, and Klingon activity became more aggressive. A group of Klingon vessels utilized the new advantage to destroy a group of Starfleet vessels on patrol simultaneously, including the USS Gagarin. Most disturbingly was that this advantage neutralized the tactics of the spore-equipped Discovery, which arrived to assist the Gagarin but could not save the stricken ship. (DIS: "Si Vis Pacem, Para Bellum")
Following the loss of the Gagarin, Discovery sought to use the natural crystal transmitter located on the planet Pahvo to use it to locate cloaked Klingon vessels. However, their actions instead led the Pahvans to transmit a signal which attracted the attention of the Klingon flagship Sarcophagus. The crew of Discovery was able to board the Klingon ship and recover Admiral Cornwell from captivity, planting beacons to penetrate the cloaking field. Using the spore drive, Discovery was able to gather enough data to complete an algorithm which would counteract the cloaking technology, and then destroyed the Klingon ship. They intended to transmit this information to Starfleet, but did not get the chance. Attempting to use the spore drive to jump to Starbase 46, the Discovery instead found itself in a parallel universe. Unbeknownst to Starfleet or the Discovery crew, the commanding officer, Gabriel Lorca did this intentionally, trapping the ship and its crew. (DIS: "Into the Forest I Go", "Despite Yourself")
At the same time, the ISS Discovery exchanged places with its counterpart, was attacked by Klingon forces and destroyed, leading Starfleet to believe that its Discovery had been lost. Without the cloak-penetrating algorithm, or the vital asset that Discovery had become, the Federation was unable to hold back the Klingon forces. In addition, having lost another unifying leader, the Klingons were no longer acting as a single force – instead, the twenty-four houses competed for dominance by seeing which house could destroy the most Federation assets. The attacks were indiscriminate, targeting hospitals, civilians and food convoys. (DIS: "The War Without, The War Within")
On stardate 4789.6, hypothermic charges were used against Kelfour VI, burning off the planet's atmosphere and instantly killing 11,000 Federation civilians. Stardate 4851.5 saw the USS Saratoga tailed by a cloaked Klingon raider as it entered Starbase 22; the raider then self-destructed, destroying the starbase. Similar attacks against Starbase 12 and Starbase 19 in the following days ultimately resulted in the loss of a third of the Federation fleet. Further assaults on the same stardate wiped out research outposts on Nivalla, Septra, and Iridin. (DIS: "The War Without, The War Within")
Nine months after the destruction of the Sarcophagus, nearly twenty percent of former Federation space was occupied by the Klingons. At this point, Discovery returned to its own universe via the mycelial network, only arriving now due to having overshot their intended return trajectory. (DIS: "What's Past Is Prologue", "The War Without, The War Within")
Although Discovery's return allowed the distribution of the algorithm, it was too late to prevent an assault on Starbase 1 by forces of House D'Ghor, who eliminated the 80,000 people aboard – including a significant part of Starfleet leadership – along with the three starships defending it. Discovery encountered the aftermath of the attack, with a House D'Ghor sigil decorating the fallen base.
With Klingon forces on the verge of striking Earth, and considering standard tactics to have failed, the Federation Council was forced to adopt a plan suggested by the stranded Terran emperor, Philippa Georgiou. As a result, it authorised Discovery to use its spore drive to jump into the subterranean caverns of Qo'noS, to map the planet's defenses and infrastructure, ahead of an all-out assault on the planet, with the aim of forcing the Klingons to retreat from Federation space. The mirror Georgiou was disguised as her counterpart and placed in command of Discovery for the duration of the mission. (DIS: "The War Without, The War Within")
The war concluded in 2257 when Georgiou planted a hydro bomb within a volcano on Qo'noS. Preventing Georgiou from detonating the device, Burnham gave the detonator to L'Rell, who used the threat of detonating the device to force the leaders of the Great Houses to accept her leadership role in the Empire. She ordered Klingon forces to halt their advance on the Federation, and then began working to continue T'Kuvma's work of uniting the various Klingon factions. (DIS: "Will You Take My Hand?")
|Battles of the Federation-Klingon War (2256-57)|
|2256: Battle of the Binary Stars • Attack on Corvan II • Battle at Pahvo|
|2257: Scorching of Kelfour VI • Attack on Starbase 22 • Attack on Starbase 12 • Attack on Starbase 19 • Attack on Nivalla • Attack on Septra • Attack on Iridin • Capture of Starbase 1|
|Sheliak Conflict • Klingon War (2256-57) • Klingon War (2267) • Cardassian War • Galen border conflicts • Tzenkethi War • Dominion cold war • Klingon War (2372-73) • Dominion War • Temporal Cold War • Klingon War (2340s-2366)|
|Federation War (2256-57) • Federation War (2267) • Klingon Civil War • Cardassian War • Dominion cold war • Federation War (2372-73) • Dominion War • Federation War (2340s-2366)|
- "The Vulcan Hello"
- "Battle at the Binary Stars"
- "Context Is for Kings"
- "The Butcher's Knife Cares Not for the Lamb's Cry"
- "Choose Your Pain"
- "Magic to Make the Sanest Man Go Mad"
- "Si Vis Pacem, Para Bellum"
- "Into the Forest I Go"
- "Despite Yourself"
- "What's Past Is Prologue"
- "The War Without, The War Within"
- "Will You Take My Hand?"