History of the Saxon War V: Alessandro Barbero's "Charlemagne: Father of a Continent"

Here is another excerpt, this one from Alessandro Barbero's Charlemagne: Father of a Continent, focussing on the religious dimension of the conflict between the Saxons and the Franks:
Charles [Charlemagne] had not set himself the declared aim of converting the Saxons to Christianity right from the very beginning. Before him, his father and grandfather had fought against them, and on each occasion, after having defeated them, they were satisfied with the payment of tribute. Einhard [c.775-840, Frankish courtier and biographer of Charlemagne] who was writing when the wounds had had time to heal and could have easily attributed Charles's campaigns beyond the Rhine to reassuring predestinations, actually asserts in very pragmatic terms that 'there were too many reasons for disturbing the peace, for example the border between us and them crossed an open plain, except in a few places where great forests or mountain chains more clearly divided the two countries. Thus murder, raids, and arson were continuously committed by one side or the other.' In the chronicler's opinion, this insecurity of the frontier with the barbarians inevitably meant that 'in the end the exasperated Franks could no longer be contented with returning each blow with another and decided to wage full-scale war against them.'

It is clear that religious motivations were inextricably bound up with political ones, as since the time of Charles Martel I [c. 688-741], Frankish swords had sustained missionary work beyond the Rhine. One of the conditions that Pepin [714-768] imposed on the defeated Saxons was the guarantee that the Frankish and Anglo-Saxon clergy working in the area would be free to continue their apostolic tasks without hindrance. It must have appeared obvious to some of these missionaries that Charles's war had a religious justification. 'If you do not accept belief in God,' Saint Lebuin told the Saxons, 'there is a king in the next country who will enter your land, conquer it, and lay waste.' But the Saxons obstinately refused to believe, so in the end that king had to make his move.
[pp. 44-45]

History of the Saxon War IV: Eric J. Goldberg's 1995 paper on "The Saxon Stellinga Reconsidered"

There were most likely several reasons for this social division with regard to attitudes toward Christianity. As with the Christianization of most Germanic peoples in late antiquity and the early Middle Ages, missionary work in its early stages was an elite business that catered to the Pagan nobility. Coverting a gens babarorum began with the kings, chieftains, and nobles and only slowly trickled down to the masses. The was the case in seventh and eighth century Saxony. The two Hewalds were martyred on their way to meet with the chieftain of a pagus [local district], and Lebuin had his nobilissimi supporters. Since the vicani of Bede's account feared that their chieftains would force Christianity on them from above, clearly they viewed the new religion as an aggressive encroachment by the nobles on their already limited political power. Also, the frilingi and lazzi probably viewed Christianity as a threat to the Marklo council, the institution through which they had a voice in Saxon politics. The council was not only an annual institution of government but a solemn Pagan religious occassion as well. At the beginning of the council the Saxons "first offered up prayers to their Gods, as is their custom, asking them to protect their country and to guide them in making decrees both useful to themselves and pleasing to the Gods." [Vita Lebuini antiqua 6, p. 793] Such close connections between religious and governmental rituals probably blurred any clear distinction between Paganism and politics at the Marklo council ... [T]he Saxons selected their military leaders by drawing lots, a procedure that also had Pagan religious significance. The frilingi and lazzi therefore probably viewed this nova cultura [Christianity] as a threat both to their ancestors' religion and to the institution of the Marklo council.

Charlemagne's conquest of Saxony was a momentous turning point that overthrew the distinctive political structures and pagan culture of the Saxons. Before the conquest, Franco-Saxon relations had been a checkered history of wars, alliances, and Saxon payments of tribute. By the 770s Charlemagne resolved to incorporate Saxony into his growing empire, apparently in order to settle once and for all border disputes with the Saxons. The result was a series of wars, raids, treaties and rebellions between 772 and 804 through which Saxony south of the Elbe was gradually incorporated into the Frankish empire ... This was a war of conquest and conversion. Charlemagne equated Saxon submission to Frankish rule with the acceptance of Christianity; according to one Frankish author, Charlemagne resolved "to persevere until the Saxons had either been overcome and subjected to the Christian religion or totally exterminated." [Annales regni Francorum s.a. 775, MGH SS 1:153]
[pp. 474-475]