While the Vikings are important for various reasons - expanding Medieval trade, settling various regions, establishing the first European contact with North America, and founding the first Russian states - they are also included here simply for their inherent interest; their raids and expansion were one of the most striking and sudden in world history.
Far more important to the historical record were the larger patterns of state and society that formed in the early Middle Ages. Above all, the feudal system would have a long legacy in forming the basis of later political structures, and the Latin Church would be the essential European intellectual and spiritual institution for centuries to come. Early medieval Europe was defined by shared cultural traits, above all having to do with religion. Despite having lost the opulence and much of the learning of Rome, medieval Europe was not a static, completely backwards place. Instead, it slowly but surely constructed an entirely new form of society in place of what had been.
Image Citations (Wikimedia Commons):
Pledge of Fealty - Myrabella
Carolingian Empire - Electionworld
Oseberg Ship - Peulle
Varangian Guard - Public Domain