The large-scale division of Charlemagne’s empire into three parts in the ninth century led to a decentralization of power at the local level. Civil wars weakened the power and prestige of kings, who could do little about regional violence. Likewise, the invasions of the ninth century, especially those of the Vikings, weakened royal authority. The Frankish kings were unable to halt the invaders, and the local aristocracy had to assume responsibility for defense. Thus, in the ninth and tenth centuries, aristocratic families increased their authority in their local territories, and distant and weak kings could not interfere. Common people turned for protection to the strongest power, the local nobles.

The most powerful nobles were those who gained warriors’ allegiance, often symbolized in an oath-swearing ceremony of homage and fealty that grew out of earlier Germanic oaths of loyalty. In this ceremony a warrior (knight) swore his loyalty as a vassal — from a Celtic term meaning “servant” — to the more powerful individual, who became his lord. In return for the vassal’s loyalty, aid, and military assistance, the lord promised him protection and material support. This support might be a place in the lord’s household but was more likely land of the vassal’s own, called a fief ( feudum in Latin). The fief, which might contain forests, churches, and towns, technically still belonged to the lord, and the vassal had only the use of it. Peasants living on a fief produced the food and other goods necessary to maintain the knight. Most legal scholars and historians have identified these personal ties of loyalty cemented by grants of land rather than allegiance to an abstract state as a political and social system they term feudalism. In the last several decades, however, increasing numbers of medieval historians have found the idea of “feudalism” problematic, because the word was a later invention and the system was so varied and changed over time. They still point to the personal relationship between lords and vassals as the key way political authority was organized and note that the church also received and granted land.

The economic power of the warrior class rested on landed estates, which were worked by peasants under a system of manorialism. Free farmers surrendered themselves and their land to the lord’s jurisdiction in exchange for protection. The land was given back to them to farm, but they were tied to the land by various payments and services. Most significantly, a peasant lost his or her freedom and became a serf, part of the lord’s permanent labor force. Unlike slaves, serfs were personally free, but they were bound to the land and unable to leave it without the lord’s permission.

By the year 800 perhaps 60 percent of the population of western Europe had been reduced to serfdom. Over the next several centuries unstable conditions and insecurity further increased the need for protection, so that by around 1000 the majority of western Europeans were serfs. While serfs ranged from the highly prosperous to the desperately poor, all had lost their freedom. In eastern Europe the transition was slower but longer lasting. Western European peasants began to escape from serfdom in the later Middle Ages, at the very point that serfs were more firmly tied to the land in eastern Europe, especially in eastern Germany, Poland, and Russia.