In the mirror universe, the repressive interstellar government dominated by Terrans from the planet
Earth. The empire ruled by terror, enforced by its fleet of starships. In 2267, members of the original U.S.S. Enterprise crew were
accidentally transported to the mirror universe, and their brief presence had a profound effect on the Terran Empire. The visiting
James Kirk convinced Spock /mirror) of the illogic of waiting for the inevitable collapse of the empire. Spock was successful in
pressing for reforms, preaching peace and disarmament, eventually becomming the empire's commander-in-chief. Unfortunately, Spock's
reforms left the empire unable to defend itself, and the Terran Empire was soon conquered by an alliance of Klingon and Cardassian
forces. With the fall of the empire, humans and Vulcans became outcasts and were forced into slavery under Alliance rule.
TOS "Mirror, Mirror"made reference to an empire that was the mirror equivalent of the Federation, but the
name Terran Empire was not used until "Crossover".
DS9 "Crossover" ; Star Trek Encyclopedia II