The correct answer to this open question is the following.
The Feudal System changed the social structure of the Middle Ages in that it impacted the social classes of the time, making merchants and peasants the poorest social class on the feudal times. They were at the very bottom of the class pyramid. Framers worked in the farm fields or were servants of nobles and the king, in exchange for some land. The basic social classes during the feudal times were the Nobles, the clergy, and the peasants.
The feudal system was different from other social structures in that it did not include a formal system of slavery, but a system of labor and servitude.