After the death of Pippin in year 768, the kingdom was divided between his sons Charlemagne and Carloman. Carloman retired to a monastery and died a short time later, leaving his brother as the only king.
Charlemagne restored a balance of power between the emperor and the pope.
From the year 772, Charlemagne undertook a long war in which he conquered and defeated the Saxons to incorporate their territories into the Frankish Empire.
This campaign was added to the practice of non-Roman Christian leaders who provoked the conversion of their neighbors by force. Frankish Catholic missionaries, along with others from Ireland and Anglo-Saxon England, had entered Saxon territory since the middle of the 8th century, resulting in an increase in clashes with the Saxons, who resisted missionary endeavors accompanied by military incursions. The main Saxon opponent of Charlemagne, Widukind, agreed to be baptized in 785, as part of peace agreements, but other Saxon leaders continued the fight.
After his victory in 782 in Verden, Charlemagne ordered the mass slaughter of thousands of pagan Saxon prisoners.
After several more uprisings, the Saxons suffered the final defeat in 804.
In order to Christianize the Saxons more effectively, Charlemagne founded several dioceses, including those of Bremen, Münster, Paderborn, and Osnabrück.
At the same time, Charlemagne conquered the Lombards, including northern Italy. He renewed the donation to the Vatican and the promise to the papacy to continue protection by the Franks.
Until 796, Charlemagne continued to expand his kingdom further to the southeast, to present-day Austria and parts of Croatia.
In the hierarchy of the Church, bishops and abbots sought the protection of the king's palace.
Charlemagne had become the leader of Western Christendom, in addition to promoting a "Carolingian Renaissance" in literary culture, thanks to his support of monasteries as centers of learning.
On Christmas Day 800, Pope Leo III crowned Charlemagne as "Emperor who rules the Roman Empire" in Rome.
After the death of Charlemagne on January 28, 814 in Aachen, he was buried in his Palatine Chapel.