The overthrow of Cardassia's military government by a civilian movement in 2372, which gave power to the Detapa Council and provided the Klingon Empire with its excuse to invade.
The fall of the Cardassian Central Command is reported in The Way of the Warrior, the opening story of the fourth season of Deep Space Nine. For centuries the military Central Command and the Obsidian Order had held real power on Cardassia while the civilian Detapa Council had almost none.
The Order's fleet was wiped out at the Omarion Nebula in 2371, and without its secret police the regime could no longer silence dissent. Cardassia sealed its borders, and news eventually emerged that a popular rising had put the Detapa Council in charge.
Chancellor Gowron and General Martok claim that only Changelings could have managed such a change, and the Klingons invade. Gul Dukat, now military adviser to the new government, carries the council members to safety aboard the Defiant. The weakened civilian state lasts until Dukat takes Cardassia into the Dominion in 2373.