What led to a new political and social order known as feudalism?

Feudalism, also called feudal system or feudality, French féodalité, historiographic construct designating the social, economic, and political conditions in western Europe during the early Middle Ages, the long stretch of time between the 5th and 12th centuries. Feudalism and the related term feudal system are labels invented long after the period to which they were applied. They refer to what those who invented them perceived as the most significant and distinctive characteristics of the early and central Middle Ages. The expressions féodalité and feudal system were coined by the beginning of the 17th century, and the English words feudality and feudalism (as well as feudal pyramid) were in use by the end of the 18th century. They were derived from the Latin words

letter d is correct.