Charlemagne is a devout Christian who wanted to improve the church by supporting the pope. He ordered priests, monks, and nuns to live strictly by Church rules. He also encouraged all his subjects to live together in perfect peace and charity. For his reward, the Pope made Charlemagne king.
Charlemagne's coronation did have lasting effects on the Church. Although in Eastern Europe, it was seen as an insult. This created the split between the Eastern Orthodox and Roman Catholic churches. Since Charlemagne and the Pope disagreed with what made him king, it also created a conflict between popes and rulers.
When Charlemagne's empire collapsed, the German lands chose a new king who typically had little power over other nobles. All of that changed once Otto the Great was crowned king. Otto wanted to increase his power so, in 962, he persuaded the pope to crown him Holy Roman Emperor.
In 1073, a monk named Hildebrand became Pope Gregory VII. He issued a list of rules that had a dramatic effect on the Holy Roman Empire. These rules claimed his authority over both Church and secular, the power to choose bishops, and even the power to remove rulers.
Gregory's rules had a direct attack on King Henry IV's own power and rights. Gregory and Henry always found new ways to get into a fight. When Gregory excommunicated Henry, his subjects had to be freed from their feudal oaths of loyalty to the emperor.
Across Europe, people took sides. Soon, the pope forgave Henry, though the conflict continued. Even though Gregory and Henry died, the arguments between rulers and popes never came to an end.