Nearly four hundred years after the fall of the Roman Empire, in 800 A.D., Charlemagne or Charles the Great of the Francs, was crowned emperor in 800 a.d. by Pope Leo III, who declared the beginning of a new Holy Roman Empire. It joined a number of kingdoms and territories in central Europe, including Bohemia, Germany, Burgandy, and Italy. Charlemagne’s family held the crown for 88 years, but then a series of civil wars broke out for 80 years over who would rule. Charlemagne is referred to by some as “the father of Europe.” He is buried in the Roman Catholic Cathedral in Aachen, Germany.
The empire re-united in 962 when Otto I was crowned emperor, claiming he was successor to Charlemagne. Thus began the continuous existence of the Holy Roman Empire for eight centuries, until 1806. The title of Holy Roman Emperor began to be used in the 13th century, and claimed power going back to the emperors of Rome. Its prime mission was ostensibly to promote and defend Christianity. However, Charles V in 1530 was the last emperor approved and crowned by the pope. After that, the emperor became more of a political rather than a religious leader during the Protestant Reformation. The empire recognized Lutheranism in 1555, and Calvinism in 1648.
The emperor was elected by the various principalities, duchys and dynasties, what today would be called tribal warlords, of Europe. Wikipedia:
The power of the emperor was limited, and while the various princes, lords, and kings of the empire were vassals and subjects who owed the emperor their allegiance, they also possessed an extent of privileges that gave them de facto sovereignty within their territories. Emperor Francis II dissolved the empire on 6 August 1806, after its defeat by Napoleon at the Battle of Austerlitz.
Historians still debate whether there was a relationship or communication between Holy Roman Emperors, beginning with Charlemagne, and the emperors of the Eastern Roman Empire, based in Constantinople, which fell in 1353, or the patriarch of the Eastern Orthodox Church, which continues until today.
The Holy Roman Empire at its peak covered parts or all of what is now Austria, Belgium, Croatia, Czech Republic, France, Germany, Italy, Liechtenstein, Luxembourg, Monaco, Netherlands, Poland, Slovenia, and Switzerland.