In 2373 Gul Dukat secretly negotiated Cardassia's entry into the Dominion, bringing Jem'Hadar fleets into the Alpha Quadrant.
In 2373 a large Jem'Hadar fleet came through the Bajoran wormhole, and the Alpha Quadrant powers prepared for an invasion. Instead the fleet went to Cardassia. Gul Dukat announced that he had negotiated for the Cardassian Union to join the Dominion, with himself as its new leader, promising to restore Cardassia's greatness.
Jem'Hadar forces quickly drove the Klingons out of Cardassian space and wiped out the Maquis. At the same time, a Changeling impersonating Dr. Bashir tried to destroy the Bajoran sun, but the plan failed. Bashir, Garak, Worf and the real General Martok escaped from a Dominion internment camp and returned to Deep Space Nine.
Facing a common danger, Gowron restored the Khitomer Accords, and the Federation and the Klingon Empire renewed their alliance. Dominion forces now had a base in the Alpha Quadrant, and the tense standoff that followed led to the outbreak of the Dominion War later that year.