I appreciate this kind of topic, but why here and not in history? Also I'm surprised you don't mention contracts, while alluding to them extensively. Feudalism, not unlike Federalism, concerns the separation of powers. This would work different ways in different places and instances. Even within one country a king or equivalent might have several different types of feudal relationships, it isn't always linear. I played lots of Paradox Interactive games which attempt to recreate some of these relationships, but my interest to learn more lead me to look up many random historical situations and circumstances.