Feudalism.

Feudalism was a combination of legal and military customs in medieval Europe that flourished between the 9th and 15th centuries. Broadly defined, it was a way of structuring society around relationships derived from the holding of land in exchange for service or labour. Although derived from the Latin word feodum or feudum, then in use, the term feudalism and the system it describes were not conceived of as a formal political system by the people living in the Middle Ages. In its classic definition, by François-Louis Ganshof, feudalism describes a set of reciprocal legal and military obligations among the warrior nobility revolving around the three key concepts of lords, vassals and fiefs.