Charlemagne's conquests became the driving force in European politics between the Muslim defeat at Poitiers and the Crusades. He dominates the military history of Medieval Europe since his empire spanned France, western Germany, and northern Italy.
Charlemagne's conquest of the Saxons was the hardest fought and most protracted of his wars. It involved 18 campaigns spread over 33 years, a great deal of lower-level fighting and the harshest final peace settlement that Charlemagne ever imposed upon a defeated foe. This was also the most important of all Charlemagne's war for the future direction and character of European history and, paradoxically, it also began the long process of uniting the German-speaking peoples.
Starting in 772 with a series of raids and incursions, the Carolingian campaign rapidly took on the character of a religious conquest, and may well have been the inspiration for the later crusades against both Islam and pagan peoples of Prussia and Livonia. Following a series of revolts and uprisings under the popular Saxon leader Widukind, Charlemagne took the field personally in the years 782 to 785 and, through a series of pitched battles and smaller actions before finally brining Widukind to heel in 785, consolidating Saxony as part of the greater Carolingian Empire.