Breen

While they had not been designated as a threat, the Breen Confederacy was one of a handful of species that had earned a place on the Starfleet Security Council’s ‘must watch’ list. While the Federation had little direct contact with the Breen, Starfleet's nominal allies, the Klingons, apparently had a long and bloody history with them. The Klingons was reluctant to share information with Starfleet, however. Klingons were embarrassed about their losses in conflict with the Breen, and the less said about that, the better, they likely thought.

Before the Dominion War, Starfleet Intelligence suspected that the Cardassians maintained an open line of communication with the Breen, and it was believed that the Breen and the Ferengi may have had informal trade agreements in place. The Romulans also appeared to have a history with the Breen; though, as with the Klingons, Starfleet had been unable to gather much in the way of confirmed details regarding relations between the two species. Starfleet's technological evaluation of the Breen was woefully incomplete, but what little they knew was that they were a species near their level of capabilities. After the Dominion War, Starfleet had assets in and near Breen space working to gather intelligence.