The Holy Roman Empire

The formation of the Holy Roman Empire was initiated by Charlemagne's coronation as "Emperor of the Romans" in 800, and consolidated by Otto I when he was crowned emperor in 962 by Pope John XII.

The Holy Roman Empire was divided into dozens—eventually hundreds—of individual entities governed by kings, dukes, counts, bishops, abbots, and other rulers, collectively known as princes, who governed their land independently from the emperor, whose power was severely restricted by these various local leaders.

The Investiture Controversy, on the surface a conflict about the appointments of religious offices, was a powerful struggle for control over who held ultimate authority, the Holy Roman Emperor or the pope.