|A Breen in 2375.|
Chancellor Mow'ga of the Klingon Empire, was one of the first modern powers to learn of the destructive force of the Breen. An entire fleet was lost when he ordered an invasion of the Breen homeworld. (DS9: "'Til Death Do Us Part")
- There may have been unofficial contacts prior to this, as they were known to exist as early as 2242. ("Roads Not Taken")
During the 24th century, Breen often pirated vessels and colonies of other races. (TNG: "Hero Worship"; DS9: "Indiscretion", "To the Death") The Breen were also known to support privateers, with the USS Shabonee battling Breen privateers in 2369 led to the ship's destruction. (Star Trek: Shabonee: "Scream") The wanted Ubessian criminal Yaghim Thau also joined forces with Breen privateers against the USS Prospect-A in 2371, with the privateers and Thau failing and being taken into custody. (Star Trek: The Prospect Chronicles: "Ramifications")
- It is unknown if the Breen were manipulated into joining the war by a Changeling, or not.
The Breen proved to be as loyal to the Dominion as the Jem'Hadar. They were more than willing to fight, even after the Federation discovered a defense against their unique power draining weapon. The war turned against them, however, and they surrendered along with all other Dominion forces at Deep Space 9. (DS9: "What You Leave Behind")
There was a massive reordering of the Confederacy following the Dominion War, the Thots, or war chiefs, that led the Confederacy into war were executed, and their bloodlines negated. (Dark Territory: "Corruption of Blood")
The Breen were a sexually segregated species. Males joined the Confederacy, while females were part of another government, called the Gynarchy. (Dark Territory: "Corruption of Blood")
Like many things about the Breen, their home planet was a mystery. Many claimed it was a "frozen wasteland," hence the need for the refrigeration suits they wear. However, there were disputing claims that the planet was temperate. (DS9: "The Changing Face of Evil")
To ensure the survival of their species, both sexes supply reproductive fluids, which were joined at neutral sites, and then the eggs were incubated and the hatchlings were brought to term and then sent to their respective worlds. (Dark Territory: "Corruption of Blood")
Without a universal translator, the Breen language sounded like a chaotic mix of electronic noises. (Star Trek: Deep Space Nine)
- It is unknown if this effect is their "true" language or simply created by their helmets.
By the mid-2370s, the Breen seemed to be at least as advanced as the Federation, if not more so.