The Dominion-Breen Alliance formed in 2375 between the Dominion and the Breen Confederacy in an initially successful attempt to gain an advantage over the Federation Alliance which ended up disillusioning the Cardassians.
To convince the Breen to join, the alliance transferred many Cardassian territories over to Breen control. As a result of this alliance, the Dominion were able to counterstrike against Federation forces in the Chin'toka system, with the help of an energy dampening weapon employed by the Breen, and return it to their control. However, the transfer of Cardassian territories, coupled with the senseless sacrifice of the Eleventh Order to the Klingons, had completely alienated Legate Damar and soon, the Breen and the Dominion were eventually forced to take action against not only the Federation Alliance, but the newly established Cardassian Liberation Front, allowing the Federation and Romulans to counteract the energy dampening weapon. The Dominion's actions against the Cardassian people only served to disillusion the Cardassian military further and eventually, only Jem'Hadar and Breen vessels were left in defense of Cardassia Prime in the final battle of the Dominion War. (DS9: "Strange Bedfellows", "The Changing Face of Evil", "What You Leave Behind")