[2] Until the fall of the Western Roman Empire, the Germanic tribes who had migrated there (with the exceptions of the Saxons, Franks, and Lombards, see below) had converted to Christianity.
During the centuries following the fall of Rome, as the East–West Schism between the dioceses loyal to the Pope of Rome in the West and those loyal to the other Patriarchs in the East grew, most of the Germanic peoples (excepting the Crimean Goths and a few other eastern groups) would gradually become strongly allied with the Catholic Church in the West, particularly as a result of the reign of Charlemagne.
The Vandals appear to have converted following their entry into the Empire in 405; for other east Germanic peoples it is possible that Visigothic missionaries played a role in their conversion, although this is unclear.
At the same time, Frankish-supported missionary activity spread across the Rhine, led by figures of the Anglo-Saxon mission such as Saint Boniface.
The process of conversion usually proceeded from the top of the social hierarchy downwards, generally peacefully, with a local ruler choosing to convert, whereupon his subjects then also nominally became Christian.
A famous case of this was king Rædwald of East Anglia, who had a Christian altar erected within his pagan temple.
During the prolonged period of Viking incursions and settlement of Anglo-Saxon England pagan ideas and religious rites made something of a comeback, mainly in the Danelaw during the 9th century and particularly in the Kingdom of Northumbria, whose last king to rule it as an independent state was Eric Bloodaxe, a Viking, probably pagan and ruler until 954 AD.
In 831, he made the missionary Ansgar archbishop of the newly created Archdiocese of Hamburg-Bremen to undertake a mission to Scandinavia, which, however, mostly failed.
The Danish king Harald Bluetooth was baptized in the late 900s, but most Danes appear to have remained pagan and converted later under English influence during the reign of Canute the Great.
Despite resistance such as the rule of the pagan Haakon Sigurdsson, Christianization was largely achieved by Olaf II (died 1030), who had converted in England.
[23] However, the decisive reason for Clovis to adopt the Christian faith was the belief that he received spiritual battle aid from Christ.
[27] Another exemplary event happened during Ansgar's second stay in Birka, when a pagan priest demanded from the locals that they not participate in the cult of the foreign Christian God.
Consequently, Christianity had to be made palatable to these Migration Age warlords as a heroic religion of conquerors, a rather straightforward task, considering the military splendour of the Roman Empire.
A fine illustration of these tendencies is the Anglo-Saxon poem Dream of the Rood, where Jesus is cast in the heroic model of a Germanic warrior, who faces his death unflinchingly and even eagerly.