GalSec was a human colony which was descended from a colony ship sent out by the Earth around the time of the Expansion. (TV: The Sontaran Experiment)
History
In the early 42nd century, Mirana's parents were born on GalSec. (AUDIO: Project Infinity)
During the following 10,000 years, they established an Empire with bases across the Galaxy. (TV: The Sontaran Experiment) A number of pre-existing colonies were taken over, and prejudice existed among GalSec colonists against the original colonies ("indigs"). (AUDIO: Wirrn Dawn)
At some point the Sontarans lured a group of GalSec soldiers to Earth with a fake distress signal in order to test their fighting capabilities. (TV: The Sontaran Experiment)
GalSec would spend a number of years at war with the Wirrn. (AUDIO: Wirrn Dawn)