The Klingon Empire or the Empire of Steel is the government of the Klingons. The Klingon Empire has conquered several species over the time of its formation.
- Dunkars: A relatively passive and accepting race who hold a position just shy of their Klingon superiors, some serving as officers.
- Slidarians: A race of huge ape/bear beings who excel at ground and hand-to-hand combat. It is notable that the Slidarian homeworld was never conquered by the Klingons, who, after their attempts at pacification, co-opted and absorbed them.
- Hilidarians: Bipedal (though capable of quadapedal movement) lizards, they were the backbone of the Klingon ground forces prior to the rise of the Slidarians. The resulting rivalry was severe enough that normally the two races do not serve together.
- Cromargs: The dwarf-like survivors of a world devastated by nuclear war, the Cromargs are excellent engineers.
- Zoolies: Literally four-eyed, Zoolies are equally capable of operating in bright sunlight and dim starlight. Zoolies make up the backbone of Klingon recon units.
- Vudar: A lizard-like race from near the galactic edge, their space is saturated by dangerous ionic radiation. Because of the hazards and difficulties of non-Vudar living in the area, they were given certain leeways allowing them to self govern. This would come back to haunt the Klingons as the Vudar would make a bid for independence at the height of the General War.
- Bargantines: Looking superficially like shorter Klingons, the Bargantines are adamant that they are related and seek to become more like their 'cousins.' Unfortunately, the Bargantines are utterly inept as a species to be warriors as that they tend to be timid, easily spooked, and rather small. On the other hand, they are superior farmers and Bargantines are the leading agriculturists on most Klingon worlds. Besides, the Bargantine's attempts at organizing military units provides amusement for the Klingons themselves.
- Vegarians: Spider-like insectoids, the Vegarians were the first former Old Kings subjects contacted and absorbed by the Klingons. Unfortunately, the Vegarians felt that they should have an equal status with them, and eventually rebelled against the Empire. The Klingons were able to quickly put down the rebellion and bombarded Vegaria back to the stone age. Vegarians were not allowed to leave their world for over a century, but were brought back at the height of the General War to act as shock troops.