As the Roman Empire changed its form and collapsed in the West, several Germanic and later Slavic peoples and the still-powerful regional noble families of the later Holy Roman Empire competed for power in different parts of Europe with one another and with the surviving eastern portion of the Roman Empire (commonly called the Byzantine Empire by modern Europeans).
The early part of the period is marked in western Europe by the greatly reduced power of centralised administration and the consequent alienation of government authority and responsibility for military organisation, taxation and law and order at successive levels to provincial and local lords supported directly from the proceeds of a portion of the territories over which they held military, political and judicial power. The later Middle Ages would see the regrowth of centralized power as countries came to be aware of their own national identities and strong rulers sought to expand the territory they organized under a central government. One well known version of this consolidation is known as the Albigensian Crusade.
This hierarchy of reciprocal obligations, known as feudalism or the feudal system, binding each man to serve his superior in return for the latter's protection made for a confusion of territorial sovereignty (as allegiances were subject to change over time, and were sometimes mutally contradictory), but the resulting ability of local arrangements to function in the absence of a strong royal power provided some resiliency in a political order distinguished by its lack of uniformity.
The spread of Christianity from the Mediterranean area and from Ireland and Scotland throughout Europe and the absence of any firm alternative ideological basis for power meant that ecclesiastics became deeply involved in government, and provided the basis for a first European "identity" in the form of a religion common to most of the continent from at least the 9th century until the separation of the Catholic and Orthodox churches (1054).
An example of this identity at work is the period loosely identified as the Crusades, during which Popes, kings, and emperors tried to draw on Christian unity to wage war on Islam, which was spreading along Europe's southern and eastern borders. Political unanimity in Europe was largely illusory, and the military support for most crusades was drawn from limited regions of Europe. Substantial areas of northern Europe also remained outside Christendom until the twelfth century or later.
It is extremely difficult to decide when the Middle Ages ended, and in fact scholars assign different starting dates for the Renaissance in different parts of Europe. Most scholars who work in 15th century Italian history, for instance, consider themselves Renaissance or Early Modern historians, while anyone working on England in the early 15th century is considered a medievalist. Others choose specific events, such as the Turkish capture of Constantinople or the end of the Anglo-French Hundred Years' War (both 1453), or the fall of Muslim Spain or Columbus's voyage to America (both 1492), or the Protestant Reformation starting 1517 to mark the period's end.
Similar differences are now emerging in connection with the start of the period. Traditionally, the Middle Ages is said to begin when the West Roman Empire formally ceased to exist in 476 CE. However, that date is not important in itself, since the West Roman Empire had been very weak for some time, while Roman culture was to survive at least in Italy for yet a few decades or more. Today, some date the beginning of the Middle Ages to the division and Christanisation of the Roman Empire (4th century) while others, like Henri Pirenne see the period to the rise of Islam (7th century) as "late Classical".
The Middle Ages in the West are often subdivided into an early period (sometimes called the "Dark Ages", at least from the fifth to eighth centuries) of shifting polities, a relatively low level of economic activity and successful incursions by non-Christian peoples (Slavs, Arabs, Scandinavians, Magyars); a middle period (the High Middle Ages) of developed institutions of lordship and vassalage, castle-building and mounted warfare, and reviving urban and commercial life; and a later period of growing royal power, the rise of commercial interests and weakening customary ties of dependence, especially after the 14th-century plague.