korinzu
And you are absolutely right. Though frankly I have no idea how expansive the faceless king or northwode pagan religions are, which is why I didn't bring them up because I didn't want to be stepping on ideas some may have with them because their is an element in the story where religion play a major role, in the form of David and team odd ball. So I decided to focus instead of what I did know were going to be fairly accurate to the theme and period the roleplay can be considered to be loosely based off of.
The first step to bring halle from the current position to a higher one is to increase their agricultural efficiency and livestock raising, IE. perishable food stuffs and associated resources. Halle's land would be better served to corn crops, where as eyre territory would be better suited for the potato, as part of the major crop for their territories temperament.
But once those have been established and improved, that will be the gateway leading to other reforms, possibly bringing in a new method for creating quality steel from limited resources, known as crucible forging, which has the characteristics of a good modern steel, which was significantly better than what our forefathers in mideival times could have achieved on their own. Tough a lot of this will take time and require some investment, but the returns would be well worth the wait.
If one side wanted to defeat the other than all one would need to do would be stifle their economy. There was a reason why traveling on roads was so dangerous, usually caravans would be stopped and either raided or burned. Usually raided as the needless sacrifice of resources would be pointless in and of itself. However the house of Eyre seems to value honor above a lot of things so they would be a bit more of a trivial sort when it comes to hiring bandits and other riff-raff in order to complete tasks not suited for actual military men.
I figure the only way to really wage a war in this time period is to take land and harvest what you can from it. The Eyre house is well situated in the north and is guarded by heavily forests surrounding their main keep. I'm sure we can harvest wood fairly easily and there may very well be villages set up for just this reason. While wood might not seem to be a very valuable resource initially when it comes to warfare, keep in mind that arrows have been known to pierce thinner variants of plate armor with use of the bodkin arrow. Not only that, but the sheer strength of the longbow is enough to destroy any band of enemy units due to its excessive strength and the lesser forms of armor men-at-arms typically wore during this time (leather and chainmail being popular).
For reference, a longbow averaged to be more than 6 feet tall and could have a draw-weight of roughly 130-150 lbs. Some people here might doubt the legitimacy of that but keep in mind that the English had trained young boys in archery and probably had a sort of ladder-system where a boy would get stronger and then get a bow with a higher draw-weight.
Theoretically, one side could rule the battlefield with nothing more than perhaps 1000 archers and 500 men-at-arms. Of course trenches would be dug and spikes placed into the ground. But theoretically this would be able to destroy any opposing force that isn't head-to-toe in thick metal armor.
Economically speaking this would be VERY easy to do from the Eyre's location as they are situated very closely to large swathes of forest and, what can be assumed, pinewood. As it is easy and one could get perhaps 20-25 bows from a single tree, you could arm a majority of your peasants and teach them how to use a bow for very little cost, mostly because a bow is a very simple weapon to use.