In the isolation and chaos of the 9th and 10th centuries, European leaders no longer attempted to restore Roman institutions, but adopted whatever would work. The result was that Europe developed a relatively new and effective set of institutions, adapted to moneyless economy, an ineffective central government, and a constant threat of armed attack be raiders such as Vikings, Magyars, and Saracens.
Feudalism is a decentralized organization that arises when central authority cannot perform its functions and when it cannot prevent the rise of local powers. In a feudal society, civil and military powers at the local level are assumed by great landowners or other people of similar wealth and prestige that are able to organize their territories and maintain orders in the absence of effective central authorities. To do that the local nobles were building relationships with other prominent individuals (retainers) in their territories. Local lords provided grants that enabled their retainers to support themselves and their families in exchange for loyal service, forming a warrior class distinct from the people of their territory. Using that military power, local leaders were seizing surrounding lands. For most part the people of these lands welcomed the change, since they were trading distance and ineffectual imperial government for the local and effective one.
At the time of established feudalism European society embraced three estates as mentioned in Bentley: "those who pray, those who fight, those who work". Though very simple, this separation clearly reflected society marked by political, social, and economic inequality.
Peasants cultivating land have been delivering a portion of their production to their superiors. This allowed local lords to secure material resources needed to maintain control over military, political, and legal affairs. When free peasants sought protection from a lord and pledged their labor and obedience in exchange for security and land to cultivate they were becoming a serfs - half free.