Date: 2372-2373

The war was triggered by Klingon fears that the Cardassian government had been infiltrated and effectively controlled by Dominion Changelings. Acting on this belief, the Klingon High Council launched a preemptive invasion of Cardassian space without presenting conclusive evidence to its former allies. Klingon forces struck quickly, overrunning Cardassian border systems and attacking key military and industrial targets. The Cardassian Union, already weakened by internal political instability and economic decline, was unable to mount an effective defense. Major worlds and installations fell under Klingon occupation, and Cardassian authority rapidly collapsed across much of its territory. The conflict widened when the United Federation of Planets refused to support the Klingon invasion. Klingon leadership accused the Federation of obstruction and possible infiltration, leading directly to open hostilities between the Klingon Empire and the Federation. As a result, the Klingon–Cardassian War became a catalyst for the broader Federation–Klingon War of 2372–2373. The war ended inconclusively when Klingon forces withdrew from Cardassian space amid growing internal dissent and the realization that the invasion had been based on flawed intelligence. In the aftermath, the Cardassian Union was left severely weakened and politically isolated, conditions that soon led it to seek protection through an alliance with the Dominion.