Charlemagne built on the foundations laid by Boniface, Charles Martel, and Pippin. Contemporary writers were vastly impressed by Charlemagne’s political campaigns to destroy the autonomy of Bavaria and his equally determined efforts against the Saxons. Under their Agilolfing dukes, who had at times led the opposition to the rising Carolingians, the Bavarians had developed an independent, southward-looking state that had close contacts with Lombard Italy and peaceful relations with the Avar kingdom to the east. Charlemagne’s conquest of the Lombards in 774 left Bavaria isolated, and in 788 Charlemagne succeeded in deposing the last Agilolfing duke, Tassilo III, and replacing him with a trusted agent. Thereafter Charlemagne used Bavaria as the staging ground for a series of campaigns in 791, 795, and 796 that destroyed the Avar kingdom.

The subjugation of the north proved much more difficult than that of the south. In the wake of the missionaries, Frankish counts and other officials moved into northeastern Frisia, raising contingents for the royal host and doing the other business of secular government. As for the Rhineland, the richer it grew, the more necessary it became to protect its hinterland, Franconia (including present-day Hessen) and Thuringia, from Saxon raids. Because there was no natural barrier behind which to hold the Saxons, this was a difficult task.

Unlike the Bavarians, the Saxons were not politically united. Their independent edhelingi (nobles) lived on estates among forest clearings, dominating the frilingi (freemen), lazzi (half-free), and unfree members of Saxon society and leading raids into the rich Frankish kingdom. Thus each of Charlemagne’s punitive expeditions, which began in 772 and lasted until 804, bit deeper into the heart of Saxony, leaving behind bitter memories of forced conversions, deportations, and massacres. These raids were inspired by religious as well as political zeal; with fire and sword, Charlemagne tried to break Saxon resistance both to Christianity and to Frankish dominance. Still, the decentralized nature of Saxon society made ultimate conquest extremely difficult. Whenever the Frankish army was occupied elsewhere, the Saxons could be counted on to revolt, to slaughter Frankish officials and priests, and to raid as far westward as they could. Charlemagne in turn would punish the offending tribes, as he did when he executed 4,500 Saxons at Verden, and garrison the defense points abandoned by the Saxons. In time, resistance to the Franks gave the Saxons a kind of unity under the leadership of Widukind, who succeeded longer than any other leader in holding together a majority of chieftains in armed resistance to the Franks. Ultimately, internal feuding led to the capitulation even of Widukind. He surrendered, was baptized, and, like Tassilo, was imprisoned in a monastery for the remainder of his life. Despite this victory, it would take another 20 years before Saxony would be finally subdued.

Charlemagne’s efforts were not limited to military repression, however. He also issued two edicts concerning the pacification and conversion of Saxony, which reveal the brutality of the process as well as its gradual success. The Capitulatio de Partibus Saxoniae (c. 785; “Capitulary for the Saxon Regions”) was intended to force the submission of the Saxons to the Franks and to Christianity, imposing the death penalty for destruction of churches, refusal of baptism, and violating the Lenten fast. The Capitulare Saxonicum (797; “Saxon Capitulary”), although not necessarily abrogating the earlier decree, replaced the harsher measures of the earlier capitulary with conversion through less brutal methods. Moreover, Frankish churchmen and aristocrats loyal to Charlemagne were introduced to secure and pacify the region. Although the northern regions that enjoyed Danish support remained outside of Frankish control, most of Saxony gradually moved into the united Frankish realm and would become a great center of political, cultural, and religious life in the 10th century.