Feudalism was a type of social system used on Earth in the Middle Ages. The Klingons went from a feudal society to a spacefaring one after being taken over by the Karsids. (TOS novel: Ishmael) In the 23rd century, Helvan civilization was in a stage of early feudalism. (TOS novel: The Prometheus Design) By the 24th century, the human colony on Lorca had developed into a feudal society. (TNG novel: Masks)