The term 'Of Serfs and Vassals' is related to the FEUDAL system, which was a form of government in medieval Europe. Feudalism was based on a hierarchical structure of land ownership and labor, with the king at the top and serfs and vassals at the bottom. Serfs were peasants who were bound to the land and had to work for their lord in exchange for protection and the use of the land. Vassals were nobles who held land from a lord in return for military service and other obligations.