The Cardassian Union has had many alliances and treaties over its history. The major ones are listed here.
UNITED FEDERATION OF PLANETS: The Cardassian Union has had a long a varied relationship with the Federation, ranging from war to alliance. What treaties the future will bring remains to be seen.
THE KLINGON EMPIRE: The Klingons have had little or no relationship with the Cardassians, until the Detapa Council started a coup, and took over control of the Union from Central Command. The Klingons saw this as the Cardassian Union being under the control of the Dominion, and declared war. Following the Breen’s state of unrest, the Klingons and Cardassians sign a mutual defence treaty.
THE ROMULAN STAR EMPIRE: The only relationship between the Cardassians and the Romulans had been the failed joint attack on the Founder’s Homeworld, orchestrated by the Tal Shiar and the Obsidian Order.
THE FERENGI ALLIANCE: For a long-time the Ferengi Alliance has been barred entering Cardassian Space, and no trade from the Ferengi has been allowed to enter the Union. Recently though some trade has been allowed, but only through middle men dealers.
THE BREEN CONFEDERACY: Cardassia had no relationship with the Breen until the Dominion War, when the Dominion signed an alliance with the Breen, forcing the Cardassians and Breen to work alongside each other. Recently the Breen have gone back to their isolationistic ways.
THE DOMINION: The Dominion of the Gamma Quadrant has been allied with the Cardassian Union twice, and both times have been devastating to the Cardassian Union and its people.
THE MAQUIS: Prior to the Dominion War, the Maquis were a painful and annoying thorn to the Cardassian Union, through their guerrilla and terrorist activities they serious damaged or destroyed a large number of military and civilian property.
THE BAJORANS: The relationship the Federation has had with the Cardassians hasn’t been nearly as long as they one the Cardassians have had with the Bajorans. With the Bajoran homeworld little over 3 light years from Cardassia Prime, it was one of the first planets to be annexed by the Union. Later and peace treaty between the two peoples was signed.
THE DEMILITARIZED ZONE: The Demilitarized Zone gave birth to the Maquis, but has been more then just a haven for terrorists.
INTERSTELLAR TRADE FEDERATION: Through this trade treaty the Cardassian come into formal contact with the Federation, the Klingons, Romulans, Kzinti, Orions, Tamarians, Gorn, the Tholians and the Hydrans.
THE UNITED CONFEDERATION OF PLANETS: Even though they were part of the original inception of what would become the UCIP, the Cardassians were forcibly expelled from the UCIP when they again signed an alliance with the Dominion, and sent spies among the UCIP and started a terrorist organization to disrupt the UCIP. Recently the UCIP and Cardassian relations have improved with the UCIP’s first joint fleet, the United Confederation Fleet offering for the Cardassians to join.
THE UNITED CONFEDERATION FLEET: UCIP’s joint fleet made up of UCIP members’ ships and crew. The Cardassians have joined the UCF but remain skeptical about its success.