The Germanic peoples are frequently blamed in popular conceptions for the "Fall" of the Roman Empire in the late 5th century. Professional historians and archaeologists have since the 1950s shifted their interpretations in such a way that the Germanic peoples are no longer seen as invading a decaying empire but as being co-opted into helping defend territory the central government could no longer adequately administer.
The presence of successor states controlled by an ethnically Germanic nobility is clear in the 6th century. How they got there is the substance of the debate today. Perhaps more important in the last decade of the 20th century and the first decade of the 21st has been the debate about exactly what "tribe" or "people" meant to these groups, whose fluidity and willingness to blend is clear from the written record. The late classical sources are especially clear for the blended nature of the Alamanni.
Individuals and small groups from Germanic tribes had long been recruited from the limes or border regions of the Roman world and had risen high in the command stucture of the army -- Odoacer, who deposed Romulus Augustus is an example. In the later empire the government began to recruit whole tribal groups under their native leaders as officers.
The Ostrogoths, Visigoths, and Vandals were converted to Christianity while they were still outside the bounds of the Empire; however, they were converted to the Arian heresy rather than to orthodox Catholicism. The one great written remnant of the Gothic language was a translation of portions of the Bible made by Ulfilas, the missionary who converted them. The Lombards were not converted until after their entrance into the Empire, but received Christianity from Arian Germanic groups.