This Present Darkness
Darkspawn are tainted creatures that dwell in the Deep Roads. When they uncover one of the Old Gods they expose it to the taint, changing it into an archdemon, which then leads them in an attack against the surface world called a Blight.
The darkspawn horde is connected through the taint, functioning as a hive-mind similar to ants. While high ranking darkspawn have a limited influence upon small groups, only an archdemon can command the entire horde.
Territory conquered by the darkspawn becomes diseased, a rotting place of twisted creatures infected by the blight. Creatures that come in close or frequent contact with the darkspawn often become diseased themselves. Examples include blight wolves and ghouls. While the blighted creatures often work alongside the darkspawn, most often because of force, their lifespan is such that their use is severely limited.