Vulcan (mirror)

In "Mirror, Mirror" Spock warns  Sulu that if anything were to happen to him that "my operatives would avenge my death, and some of them are Vulcans." Prior to the airing of "In a Mirror, Darkly" several theories were put forth to explain how mirror universe Vulcans became what they were. The Best of Trek suggests Surak died as an infant so that Vulcans never adopted a way of logic and peace, and Diane Duane basically used this viewpoint in her novel Dark Mirror. The Mirror Universe Trilogy had Vulcan adopt Surak's teachings, but at First Contact with Earth advanced knowledge of the Borg threat caused both Earth and Vulcan to adopt a militaristic approach to space.