Feudalism was the system of protections and loyalties in the Middle Ages. As the Roman Empire began to fall, the Roman army was no longer able to protect the peasants, and so the peasants called upon the rich -- called lords -- to protect them. In return, the peasants became serfs or were otherwise bound to the lords. Serfs were, in essence, the same as slaves, except for the fact that they could not be sold.
Regular Websites
Feudalism and Knights in Medieval Europe
Examines the roles of the Vikings, the Magyars, and the Muslims in feudal Europe. Provides time lines and thematic essays on the topic and displays maps which are relevant. - Feudalism and Knights in Medieval Europe
http://www.metmuseum.org/toah/hd/feud/hd_feud.htm
Contains a discussion of feudalism as it pertains to living in medieval times, including short entries about feudal ties, a vassal's obligations versus a lord's obligations, manors, and a serf's life. - Feudalism and Medieval Life
http://www.britainexpress.com/History/Feudalism_and_Medieval_life.htm
Provides details about the history of feudalism, including the reasons for the system in the first place, the structure itself, and what it was like to live in feudal Europe between the tenth and fifteenth centuries. - History World
http://www.historyworld.net/wrldhis/PlainTextHistories.asp?historyid=ac35
The topic of this website is the Middle Ages in general and the feudal system of that era specifically. Included here is the "pecking order" of the system and what life was like as a serf. - Medieval Feudal System
http://www.castles.me.uk/medieval-feudal-system.htm
The Feudal Structure of the Medieval World
Focuses on the upper and peasant classes of the medieval era and how the feudal structure affected the world, as well as the resulting security of the arrangement. - The Feudal Structure of the Medieval World
http://library.thinkquest.org/10949/fief/hifeudal.html