Date: 2372-2373

The Klingon High Council became convinced that the Cardassian Union government had been infiltrated and effectively replaced by Dominion Changelings. When the Federation refused to support a preemptive Klingon invasion of Cardassia, relations between the longtime allies collapsed. Hostilities began when Klingon forces launched large-scale attacks against Cardassian territory and subsequently against Federation installations that opposed them. The Klingons assaulted Federation starbases, colonies, and shipping lanes, marking the first open war between the two powers in decades. Starfleet, caught off guard by the sudden betrayal, was forced into a defensive posture while attempting to avoid a wider regional collapse. The conflict widened as Klingon forces attacked Deep Space Nine, attempting to seize control of the strategically vital Bajoran Wormhole. Although the station successfully repelled the assault, the battle confirmed that the war had escalated beyond a limited dispute. Throughout the fighting, Klingon intelligence failures and internal political manipulation, particularly by Gowron, further destabilized the Empire’s decision-making. The war ended after clear evidence emerged that the Klingon invasion of Cardassia had been based on false assumptions, a Changeling had infiltrated them and were the ones that encouraged the war. The growing threat of the Dominion became impossible to ignore, both sides moved toward reconciliation. The Klingon Empire formally withdrew from Federation space and restored diplomatic relations, rejoining the alliance shortly thereafter.