Feudalism

Things have begun to stabilize in your world as Charlemagne has assumed the throne as King of the Franks and managed to unite most of Europe under his rule. As the years progress though, things are not always easy because Vikings from the north are attempting to pillage and plunder manors that do not have good protection. You are afraid your land might be next on their list! Can you help create a system that offers protection for both the king and his people?