But, who is this enemy?  Where do they come from?  What grievance do they have with Havenlock?  What is their army composed of?<br/><hr/><br/>I say to put things on their heads. Maybe they came from one of the neighboring nations and Hux has gone back on his word to them and imprisoned someone important to that side at the behest of that side's enemy. Now one side wants to free that person (and the other prisoners) while the other is coming to murderate everyone. The army could just be standard human units with some artilley like heavy ballista to batter the walls with.  Or it could simply be that the prison is in a strategically important area and one of the armies around them wants to use it as a expansion foothold. The prisoners have nothing to do it; just caught in the middle.