It has been famously pointed out that the Holy Roman Empire was neither holy, nor Roman, but it was also not an empire in the sense people expect when hearing the term. In theory, the emperor was the highest prince in Christendom, and his dominion extended the length and breadth of Western Europe. The empire had been created by the papacy in 801 when Pope Leo III famously crowned the supposedly unwitting Charlemagne in Saint Peter's Basilica, intending to recreate the Western Roman Empire. In truth, the imperial power did not extend beyond central Europe, which by the beginning of the 16th century included Germany, northern Italy and the Netherlands. Even in these lands, however, the emperor struggled to command obedience. His dominion over northern Italy was theoretical only, the cities of the Netherlands were deeply conscious of their ancient rights and privileges, and Germany had long ceased to be compliant. The latter had become a collection of principalities, dukedoms and bishoprics which vied with each other and pursued their own agendas. They were, however, united in only one sense: denying the emperor power and resisting attempts to centralize the government.

At the same time, major religious changes were happening within Germany in the early 16th century. Born shortly after the invention of the printing press, Martin Luther became one of Europe's best selling authors, along with others like Erasmus, and his theology was mass produced across Europe. He strongly disputed the claim that freedom from God's punishment of sin could be purchased with money, known as indulgences, and he confronted indulgence salesman Johann Tetzel with his Ninety-Five Theses in 1517, one of the most important religious writings of all time. His refusal to retract all of his writings at the demand of Pope Leo X in 1520 and the Holy Roman Emperor Charles V at the Diet of Worms in 1521 resulted in his excommunication by the Pope and condemnation as an outlaw.