The terms feudalism and feudal system were generally applied to the early and central Middle Ages—the period from the 5th century, when central political authority in the Western empire disappeared, to the 12th century, when kingdoms began to emerge as effective centralized units of government. For a relatively brief period, from the mid-8th to the early 9th century, the Carolingian (Carolingian dynasty) rulers, especially Pippin (Pippin I) (reigned 751–768) and Charlemagne (reigned 768/771–814), had remarkable success in creating and maintaining a relatively unified empire. Before and afterward, however, political units were fragmented and political authority diffused. The mightier of the later Carolingians attempted to regulate local magnates and enlist them in their service, but the power of local elites was never effaced. In the absence of forceful kings and emperors, local lords expanded the territory subject to them and intensified their control over the people living there. In many areas the term feudum, as well as the terms beneficium (benefice) and casamentum, came to be used to describe a form of property holding. The holdings these terms denoted have often been considered essentially dependent tenures, over which their holders' rights were notably limited. As the words were used in documents of the period, however, the characteristics of the holdings to which they were applied are difficult to distinguish from those of tenures designated by such words as allodium, which has generally been translated as “freehold property.”

As defined by scholars in the 17th century, the medieval “feudal system” was characterized by the absence of public authority and the exercise by local lords of administrative and judicial functions formerly (and later) performed by centralized governments; general disorder and endemic conflict; and the prevalence of bonds between lords and free dependents (vassals (vassal)), which were forged by the lords' bestowal of property called “fiefs” and by their reception of homage from the vassals. These bonds entailed the rendering of services by vassals to their lords (military obligations, counsel, financial support) and the lords' obligation to protect and respect their vassals. These characteristics were in part deduced from medieval documents and chronicles, but they were interpreted in light of 17th-century practices and semantics. Learned legal commentaries on the laws governing the property called “fiefs” also affected interpretation of the sources. These commentaries, produced since the 13th century, focused on legal theory and on rules derived from actual disputes and hypothetical cases. They did not include (nor were they intended to provide) dispassionate analysis of historical development. Legal commentators in the 16th century had prepared the way for the elaboration of the feudal construct by formulating the idea, loosely derived from the Libri feudorum, of a single feudal law, which they presented as being spread throughout Europe during the early Middle Ages.

The terms feudalism and feudal system enabled historians to deal summarily with a long span of European history whose complexities were—and remain—confusing. The Roman Empire and the various emperors' accomplishments provided a key to understanding Roman history, and the reemergence of states and strong rulers in the 12th century again furnished manageable focal points for historical narrative, particularly since medieval states and governmental practices can be presented as antecedents of modern nations and institutions. The feudal construct neatly filled the gap between the 5th and the 12th century. Although Charlemagne may seem an anomaly in this evolution, he was presented as “sowing the seeds” from which feudalism emerged. A variety of Roman, barbarian, and Carolingian institutions were considered antecedents of feudal practices: Roman lordship and clientage, barbarian war chiefdoms and bands, grants of lands to soldiers and to officeholders, and oaths of loyalty and fidelity. In the 17th century, as later, the high point of feudalism was located in the 11th century. Later rulers who adopted and adapted feudal institutions to increase their power were labeled “feudal” and their governments called “feudal monarchies.” Despite the survival of institutions and practices associated with the medieval feudal system in the 17th century, historians of that time presented medieval feudalism and the feudal system as declining in importance in the 14th and 15th centuries. This period was later dubbed an age of “bastard feudalism” because of the use of salaries and written contracts between lords and dependents.

Those who formulated the concept of feudalism were affected by the search for simplicity and order in the universe associated with the work of Nicolaus Copernicus (Copernicus, Nicolaus) (1473–1543) and especially Isaac Newton (Newton, Sir Isaac) (1642–1727). Historians and philosophers were persuaded that if the universe operated systematically, so too must societies. In the 16th century some students of the law and customs of the fief declared that feudal institutions were universal and maintained that feudal systems had existed in Rome, Persia, and Judaea. The philosopher Giambattista Vico (Vico, Giambattista) (1668–1744) considered the fief one of humankind's eternal institutions. Adopting a similar position, Voltaire (1694–1778) contested the judgment of Montesquieu (Montesquieu, Charles-Louis de Secondat, baron de La Brède et de) (1689–1755) that the appearance of feudal laws was a unique historical event. The philosophical historians of 18th-century Scotland searched for feudalism outside western Europe, and they expanded the construct's field of significance to encompass peasants as well as lords. Adam Smith (Smith, Adam) (1723–90) presented feudal government as a stage of social development characterized by the absence of commerce and by the use of semi-free labour to cultivate land. Smith's student John Millar (1735–1801) found “the outlines of the feudal policy” in Asia and Africa. The association popularly made between the feudal construct and ignorance and barbarism fostered its extension to regions which Europeans scarcely knew and which they considered backward and primitive.

Following Millar's precedent, some later historians continued to look for feudal institutions in times and places outside medieval Europe, most notably Japan. These efforts, predictably, resulted in misconceptions and misunderstanding. Historians using the feudal model for comparative purposes emphasized those characteristics which resemble or seem to resemble Western feudal practices and neglected other, dissimilar aspects, some of which were uniquely significant in shaping the evolution of the areas in question. For Westerners, the use of the feudal model necessarily created a deceptive sense of familiarity with societies that are different from their own.

Marx and Engels's model of Western historical development indicates how popular the feudal construct had become by the middle of the 19th century. Their modification of the construct to serve their own purposes demonstrates its pliancy. However, they were not unique in having shaped the feudal construct to suit their particular perspective. The Australian medieval historian John O. Ward isolated 10 different sets of phenomena that historians had associated with feudalism. Some employed narrow legalistic definitions like those elaborated by 16th-century lawyers. Others, following the English historian Thomas Madox (Madox, Thomas) (1666–1726/27) and the French historian Marc Bloch (Bloch, Marc) (1886–1944), equated feudalism with feudal society. They saw feudalism as encompassing many if not most aspects of medieval society: peasants, whether free, unfree, or semi-free; a ruling warrior class with subordinates compensated for military service by grants of land rather than money; fragmentation of power; and disorder—yet with the family and the state retaining their importance. The American historian Joseph R. Strayer (1904–87) laid special emphasis on the splintering of political and public power and authority, and he believed that systematized feudal institutions and customs were compatible with the formation of large political units, which he viewed as recognizable precursors of contemporary nation-states. Although Bloch and Strayer employed the feudal construct throughout their careers, both admitted the idiosyncrasy of the various definitions of the feudal labels that have been proposed, and both acknowledged that focusing on the construct inevitably obscures the human beings, both individuals and groups, whose actions historians are dedicated to comprehending.

From the time of the French historian Louis Chantereau Le Febvre (1588–1658), questions were raised concerning the extent to which the feudal construct oversimplified and distorted the historical realities it was intended to capture. Chantereau Le Febvre denounced as futile the attempts of his contemporaries to deduce general rules from uncertain principles. He stressed the necessity of studying authentic acts and working “historically,” implying thereby that his contemporaries were not working in this fashion. He cautioned against reducing the great variety of fiefs to a single type, because each fief was different from the others. Despite Chantereau Le Febvre's reservations, in the end he succumbed to current fashion and endorsed a simplified picture of feudal institutions. He did, however, edit and publish medieval documents demonstrating the difficulty of attaching precise meanings to such words as feudum and allodium.

Many modern historians have attempted to follow Chantereau Le Febvre's admonitions and have studied these words and others, such as vassus (“vassal”), homo (“man”), and fidelis (“the faithful”), which figured centrally in the classic definitions of the feudal construct. By examining the contexts in which key words appear in a host of medieval acts and chronicles, they have demonstrated the wide range of meanings these words possessed and the difficulty of formulating simple and precise definitions of any of them. It is clear that in the Middle Ages those who fought (like those who farmed) were rewarded in different ways and were sometimes paid in money. Land was owned, controlled, and held in a variety of ways. Similarly, enterprising individuals used a range of tactics to augment their lands and wealth and increase their power. Standardization and regularization of tenurial and territorial bonds and of ceremonies such as homage accompanied the development of centralized government, as lords and kings utilized these devices (and many others) to buttress and extend their authority.

The extent to which surrender of property to a lord as a fief limited control and rights over the property has been investigated, as has the importance of such acts in creating ties between family groups that could be repeatedly renewed. The difficulty and danger of drawing sharp distinctions between the ceremonial practices of the nobility and the peasantry have been recognized, so too the importance of urban and parochial communities and the significance of spiritual and economic links between religious establishments and the laity. In studying the settlement of disputes, historians have emphasized the continuing importance of mediation and of judgments given by free men, especially members of the secular and ecclesiastical elite. Lordship has emerged as a more centrally important topic than the feudum. The quality of lords' relationships with their dependents, free and unfree, has been debated, with some historians stressing the predatory, exploitative aspects of lordship and others emphasizing its protective, beneficial features.

Increased knowledge of the Middle Ages and greater sophistication regarding the constructs (and periods) that scholars have created in attempting to comprehend the past have sparked the search for appropriate terms to describe human institutions and societies. Although the feudal labels have lost their validity as terms to designate the realities of medieval society, they provide insight into the thought processes and assumptions of the lawyers and historians who formulated and utilized them between the 16th and the 20th century.