Not much is known about The Besieging Army, but the soldiers do talk when they come back from the now-irregular skirmishes. They wield no bows or spears, only using slings and swords. While they hide their faces behind sleek helmets, they seem to be taller and thinner of stature than our citizens.
All we can say for sure is that this isn't a civil war—so that's a small comfort, at least.