The Terran Confederacy was an interstellar hegemony established by one of the three original Terran colonies in the Koprulu Sector.
Before the Great War, it was one of the most powerful and heavily armed powers known. Due to rampant corruption and excessive use of force, the Confederacy found itself at odds with many rebel factions. Some of their amoral tactics included experimentation of the Zerg as a weapon using fringe worlds as test beds.
For more information see the Terran Confederacy on the parent site