Eberron: Equilibrium's End
The Ashbound are a sect of Eldeen druids who believe that the use of magic represents a perversion of the natural order. Though some Ashbound use peaceful means to spread their message, many see violence as the only way to achieve their ends.
Marda believes that the presence of The Ashbound in Hatheril is indicative of their involvement in the bombings of Lightning Rail routes. Similarly, The Ashbound seem to have been pulling the strings of The Black Fangs, supplying them with resources to achieve whatever goals they may have had in Hatheril.