In A Nutshell:

The Early Middle Ages was the period of European history lasting from the 5th century to the 10th century. The Early Middle Ages followed the decline of the Western Roman Empire and preceded the High Middle Ages (c. 1001–1300). The period saw a continuation of trends begun during late classical antiquity, including population decline, especially in urban centres, a decline of trade, and increased immigration. The period has been labelled the "Dark Ages", a characterization highlighting the relative scarcity of literary and cultural output from this time, especially in Western Europe. However, the Eastern Roman Empire, or Byzantine Empire, continued to survive, and in the 7th century the Islamic caliphates conquered swaths of formerly Roman territory.

Many of these trends were reversed later in the period. In 800 the title of emperor was revived in Western Europe by Charlemagne, whose Carolingian Empire greatly affected later European social structure and history. Europe experienced a return to systematic agriculture in the form of the feudal system, which introduced such innovations as three-field planting and the heavy plow. Barbarian migration stabilized in much of Europe, though the north was greatly affected by the Viking expansion.