However, prior to the war's commencement, Carloman died. Thus, Charlemagne gained complete power of the kingdom. Once in power, Charlemagne used it to increase his area of reign and thus build the first European empire since the fall of the Roman Empire. The first battle in this life-long battle of conquest was over Lombardy. Seeing himself as the servant of the Pope, Charlemagne let his power be influenced by the Pope's quest for power. Thus, when Pope Hadrian I took succession he demanded the return of various cities in the former area of Ravenna from Desiderius. When Desiderius refused the request and instead began taking other papal cities and moving an invasion towards Rome, Hadrian personally requested that Charlemagne enforce the policies of his father. Charlemagne agreed with the Pope and led an invasion over the Alps in 773, successfully forcing the Lombards back to Pavia before laying siege to that and being crowned king.

Charlemagne was involved in non-stop battles throughout his reign. One of his biggest and longest lasting campaigns was his thirty year war against the Saxons, which he eventually conquered and converted the people to Roman Catholicism. At the same time, Charlemagne was also waging successful campaigns in Italy, earning himself the title of King there also. He also led a Spanish campaign, an area ruled by the Muslim Moorish rulers. The Moors, who were under attack by another Muslim sect, made an offer to Charlemagne where they would pay him homage as the great King of the Franks in exchange for military support. Charlemagne saw this as an opportunity, again being influence by the Pope and his Catholicism, to expand Christianity and his own personal power....

This battle turned out to be Charlemagne's most difficult and, after not succeeding as quickly as he planned and in fear of risking defeat, he instead decided to retreat back home. He realized that he could not trust neither the Moors or the Basques, his supposed allies. During his retreat, his army was surprise attacked by the Basques, killing many of Charlemagne's most highly regarded warriors and leaders. In the end, the Spanish campaign was a complete disaster and a total failure.
Clearly, Charlemagne's use of power was highly influenced by two things: his desire to expand Catholicism and his desire to expand his own personal power. Thus, Charlemagne also took steps to ensure that his empire did not expand to a point he would be unable to control. To preserve his power, he strategically appointed his sons to various positions of authority, giving them the kingdoms of Neustria, Italy and Aquitaine.

The epitome of Charlemagne's purposes of power came to its climax in 800 when Pope Leo III crowned him Imperator Romanorum, or Emperor of the Romans in Saint Peter's Basilica. Thus Charlemagne was coroneted as part of the pope's attempt to transfer the office from Constantinople (where it was transferred at the time of the split of the Roman Empire) back to Rome. Charlemagne now had the title of the renewer of the Western Roman Empire, which ended in 476. Careful to avoid conflicts with the Byzantine Empire, or the Eastern Roman Empire, Charles changed his title to Roman Emperor ruling the Empire, as Emperor of the Romans was a title reserved for the Byzantines.

Barbero, Alessandro. Charlemagne: Father of a Continent. Berkley: University of California Press, 2004.