Federation-Klingon War (2372-73)

The Federation-Klingon War (2372-73) was a brief but brutal conflict fought between the United Federation of Planets and the Klingon Empire from 2372-2373.

Prelude
In the early 2370s, the Alpha Quadrant powers faced an entirely new and dangerous threat from the Gamma Quadrant, the Dominion. Following the disastrous Battle of the Omarion Nebula in 2371, a coup on Cardassia shifted power from Central Command to civilian authorities in the Detapa Council. Convinced that this coup had been engineered by the Dominion, Klingon Chancellor Gowron ordered an invasion of the Cardassian Union in early 2372. As the Federation Council condemned this invasion and refused to take part, Gowron withdrew from the Khitomer Accords, thereby ending the peace treaty between the two powers. Throughout the year, the Klingons showed increased aggressiveness against other powers, including the Cardassians, the Romulans, the Bajorans, and the Federation. Tensions rose so much, that in late 2372 Federation worlds near the Klingon border already called for a preemptive strike against the Empire. 

Open War
The actual war began when Chancellor Gowron, instigated by a Founder posing as his trusted aide General Martok, issued an ultimatum demanding the Federation's complete withdrawal from the Archanis sector within ten days. 

The Federation refused and the Klingons began a full-scale attack on the Federation, committing all available military resources to the war. In the ensuing fighting, the Federation proved almost completely unprepared for a sustained conflict on the 'secure' Klingon border, several dozen starships and border worlds were attacked during the fighting across a wide swath of territory from Archanis all the way to the Bajor sector. After some time however, Starfleet managed to slow down the Klingon advance; furthermore, it was implied by the Martok changeling that the Federation would eventually manage to rally and push back the Klingon advance with steadily increasing proportions of losses to the Klingon Defense fleet.

Acting on information provided by Odo, who had recently been in the Great Link, the Federation became convinced that Gowron had been replaced by a Founder, who was fighting the war to weaken the two former allies pending a full invasion. A covert operations team, led by Captain Benjamin Sisko, infiltrated the Klingon military headquarters on Ty'Gokor with the intention of exposing the Gowron changeling. However, it was ultimately revealed that Martok, not Gowron, was the real shapeshifter, and that Odo's information had merely been planted in the hopes of further worsening Federation-Klingon relations. For the service of exposing the enemy spy, Captain Sisko's team was allowed to leave Klingon space unhindered, and Gowron convinced the Klingon High Council to call for a cease-fire. 

The ceasefire was broken briefly a few weeks later, when Klingon troops attacked Ajilon Prime, supposedly as revenge for the Federation victory on Ganalda IV. Starfleet also prepared to retake still-occupied Archanis, an effort led by the USS Tecumseh and the USS Rutledge. The ceasefire was reinstated a few days later, but not without heavy losses both on Ajilon Prime and in space (the USS Farragut (NCC-60597)). Hostilities were only completely ended when Chancellor Gowron agreed to re-sign the Khitomer Accords in the face of the Dominion invasion six months later. 

Föderal-Klingonischer Krieg (2372/73) 第二次連邦・クリンゴン戦争 Federatie-Klingon Oorlog (2372-73)