Early in the Carreon's age of interstellar exploration, they made first contact with the Deltans, and fell into conflict with that race over control of the resource-rich worlds between their two systems. Treaties between the Carreon and Deltans left these worlds largely undeveloped; however, when a series of Iconian gateways opened across the galaxy in 2376, both powers were given instantaneous access to one particularly rich world. A shooting war was avoided by the presence of the USS Enterprise. (TNG - Gateways novel: Doors Into Chaos)
The Carreon designed the water reclamation systems on the planet Gault. When the Deltans' system became compromised, they wanted to use the same design. The Carreons, non-members of the Federation, refused to allow them to do so. (TNG novel: A Time for War, A Time for Peace)
Newly-elected Federation President Nanietta Bacco urged the two governments to handle the matter between themselves, but after close to four months, Bacco accused the Carreon ambassador, Alfear Yorgas, of negotiating in bad faith, and threatened war against Carrea if an agreement wasn't reached immediately. The Carreon eventually granted the Deltans their reclamation system in exchange for the establishment of a scientific base on a Deltan-claimed planet, Brannik IV. (ST novel: Articles of the Federation)
- Articles indicates that the Carreon and Deltans have had interactions for "centuries," which would apparently place their initial contact in the 22nd century.