There are three things about the Holy Roman Empire that every high school student is taught: it was neither holy, Roman, nor an empire. But it tried to be. Since it no longer appears on modern maps, we forgot how much the Holy Roman Empire impacted European politics for centuries.
On Christmas Day 800, Pope Leo III crowned Charlemagne as emperor. The idea of an emperor was that Charlemagne’s rule was a continuation of the old Roman Empire in the West, which had been effectively demolished for three centuries. Rome still lived. The title was elective; the emperor was selected from the nobility in Europe. There was no capital city, and the kingdom consisted of hundreds of decentralized domains. Other rulers maintained their own land and had de facto independence, but they owed allegiance to the emperor.
Like other nobles, the Holy Roman Emperor often appointed his own bishops and had control over who held ecclesiastical positions within his kingdom, up to the papacy. Non-firstborn sons of nobility often were given high positions in the church. As part of his large reform plan, Pope Gregory VII tried to reform the investiture system, placing power back in the church. The College of Cardinals was created in 1059; church officials would determine who was pope, and from there, the Church would curtail secular investiture and simony in Europe.
The struggle between Church and kingdoms continued. The Concordat of Worms in 1122 allowed kings to invest bishops with secular authorities within their kingdoms, but only the Church could invest sacred authority. This left bishops with split loyalties: one to a king and one to the pope. Kings maintained rights over their kingdoms (including some added tax benefits), and the papacy maintained its place outside the control of the Holy Roman Emperor (and got some added tax benefits). Kings struggled to have control over their individual kingdoms while still maintaining strength in unity, which meant the good graces of the Holy Roman Empire and the Church.
By the Late Middle Ages, the concept of power was becoming more attached to money and land (which could be taxed for money) rather than birthright and titles won in war. The Holy Roman Empire, an empire of scattered landholdings across Europe, struggled to maintain control in an era of land consolidations and the early rise of the nation-state. In the late 1400s, Maximilian I tried to reform the empire, levying new taxes, creating a supreme court, and forming foreign policy legislation with other kings at the Diet of Worms of 1495. But the reforms only kept the empire one of many players on the European stage.
By the turn of the sixteenth century, Germany was comprised of several kingdoms. The nobles were seeing increased wealth, and the concept of a nation-state was taking shape. These states didn’t really see the need of a unifying empire, or Church for that matter. They wanted total control within their borders, and they had the strength to fight for it. The power of the Holy Roman Empire was weakened, and nobles were losing interest in pledging loyalty to outside rulers, be they emperor or pope.