Quoted from the Memory Alpha article on the Dominion War:
The war was officially ended with the signing of the Treaty of Bajor, and all Dominion forces returned to the Gamma Quadrant, with the exception of the head Founder, who was to stand trial for war crimes. (DS9: "What You Leave Behind") Foremost in the aftermath, however, was the state of Cardassia Prime. Eight hundred million civilians were dead, and the entire Cardassian Union was in danger of total collapse. The Alpha Quadrant had lost a major power, and the effects on galactic politics would continue to be seen for many years to come.