Margaret Deanesley 
History of Early Medieval Europe [PDF ebook] 
From 476-911

Originally published in 1956, A History of Early Medieval Europe traces the changes that took place in Europe between the fifth and tenth centuries, a time of social and political upheaval, when the organization of the Roman Empire, with its single emperor, army and civil service, was replaced by the divided Europe of the Germanic kingdom in the west and the Byzantine empire in the east.