What was the name of the system of protection devised in medieval Europe when the nobles were given land in exchange for military service?

The system of protection devised in medieval Europe was called feudalism. In this hierarchical structure, nobles were granted land, known as fiefs, by a king or higher authority in exchange for military service and loyalty. This arrangement created a network of obligations and protections among different social classes, primarily between lords and vassals. Feudalism played a crucial role in the organization of society during the Middle Ages.