During this period, slaves did not exist, instead, peasants (or farmers) came into being, the whole society in the Middle Ages was made up of two classes—nobles and peasants. Nobles are the rulers of the state with a great number of privileges and properties. They are the lords of the nation and must be loyal to the king of the country, and they are offspring of meritorious statesmen, and inherited their ancestors’ title. Such noble families, proud of their independence and ancestry, maintained their position through complex kin networks, mutual defense pacts with other noble, and control of castles, from which they could dominate the surrounding countryside. By the twelfth century, nobles lived safely behind the castle walls, often even independent of the local counts, dukes, and kings. This lesser nobility absorbed control of such traditionally public power as justice, peace, and taxation.

The noble lifestyle required wealth, and wealth meant land. The nobility was essential a society of heirs who had inherited not only land, but also the serfs who worked their manors. Lesser nobles acquired additional property from great nobles and from ecclesiastical institutions in return for binding contracts of mutual assistance.  

And because of the endless mass in medieval Europe after the Carolingian Dynasty had broken up, the ambitious rulers wanted to earn more interests, such as land, money, power, subjects, some of whom longed to unite the whole continent and to be crowned as the great king. So wars, battles, conflicts, fighting among these European nations never came to an end. Assassinations, murders, negotiation and concession were seen more frequently in splendid castles or magnificent palaces. Nearly every person at that time had no a sense of security, that is why nowadays we call it the “Dark Age”.

2.2 The Economy in Medieval Europe
With the emergency of the feudalism, the household emerged as the primary unit of social and economic organization. Across much of northwestern Europe, in particular in France in the eleventh
Century, the various gradations in status disappeared, and the peasantry formed a homogeneous social category loosely described as serfs. Although they were not slaves in a legal sense, their degraded statue, their limited access to public courts of laws, and their enormous dependency on their lords left them a situation similar to that of the slaves in the past. Each year, peasants paid their lords certain fixed portions of their meager harvests. In addition, they had to work a certain number of days on the demesne, or reserve of the lords, the produce of which went directly to him for his use or sale, this kind of economy is called “manorial economy”.

Most peasants led lives of constant insecurity. They were poorly housed, clothed, and fed; subject to the constant scrutiny of their lords; and defenseless against natural or human-made disasters. Their homes were typically constructed of mud and wood and shared with their most valuable domestic animals. These huts usually had no windows and, until the sixteenth century, no chimneys. Smoke from the open hearth escaped through a hole in the roof.

Peasants’ houses were clustered in the villages on manors or large estates. In some parts of the Europe, this was the result of their lords’ desire to keep a close eye on his labor supply. In these villages, peasants were obliged to have disputes settled in the lords’ court, to grind their grain in the lords’ mill, and to bake their bread in the lords’ oven—all primary sources of revenue for the lord. The same sort of monopoly applied to the Church. Villages had to contribute a tenth of their revenues to the Church and to make donations in order to receive the sacraments. In some villages, these payments may have actually gone to the Church, but usually they went to the lords, too.

2.3 The Religion in Medieval Europe 浅析欧洲中世纪骑士精神(4):http://www.youerw.com/yingyu/lunwen_12420.html