The 2372 Klingon attack on Deep Space Nine after the Federation refused to back Gowron's invasion of Cardassia, told in The Way of the Warrior.
In 2372, Chancellor Gowron became convinced that changelings had taken over the new civilian government of Cardassia and launched an invasion of Cardassian space. Worf refused to support him, and the Federation condemned the attack. Gowron withdrew the Empire from the Khitomer Accords.
In the Deep Space Nine episode The Way of the Warrior, Captain Sisko takes the Defiant to rescue the members of the Cardassian Detapa Council, with Gul Dukat's help, and brings them to the station. Gowron then attacks Deep Space Nine with a large fleet. The station's newly upgraded weapons and shields hold off the first wave, but Klingon troops beam aboard and fight the crew in the corridors.
Sisko convinces Gowron that Federation ships are on the way and that continuing the attack will only weaken both powers against the Dominion. Gowron calls off the assault, though the alliance stays broken for a time. Worf then joins the Deep Space Nine crew as the station's strategic operations officer.