In the Early Middle Ages, depopulation, deurbanization, and barbarian invasions, which began in Late Antiquity, continued. The barbarian invaders formed new kingdoms in the remains of the Western Roman Empire. In the 7th century North Africa and the Middle East, once part of the Eastern Roman Empire (the Byzantine Empire), became an Islamic Empire after conquest by Muhammad's successors. Although there were substantial changes in society and political structures, the break with Antiquity was not complete. The still-sizeable Byzantine Empire survived and remained a major power. The empire's law code, the Code of Justinian, was widely admired later in the Middle Ages. In the West, most kingdoms incorporated extant Roman institutions, while monasteries were founded as Christianity expanded in western Europe. The Franks, under the Carolingian dynasty, established an empire covering much of western Europe; the Carolingian Empire endured until the 9th century, when it succumbed to the pressures of invasion—the Vikings from the north, the Magyars from the east, and the Saracens from the south.
During the High Middle Ages, which began after AD 1000, the population of Europe increased greatly as technological and agricultural innovations allowed trade to flourish and crop yields to increase. Manorialism—the organization of peasants into villages that owed rent and labor services to the nobles; and feudalism—the political structure whereby knights and lower-status nobles owed military service