At the beginning of the 1930s, the Reformation spread to many territories and imperial cities of the Holy Roman Empire. This raised the question of the legal status of Protestantism, whose teachings were officially considered heresy. In the eyes of many Catholics, the Roman-German Emperor had to counter the spread of such "heresies". As a result of the Imperial Diet of Augsburg in 1530, nothing changed in the imperial legal position of Protestantism, especially since the Confessio Augustana, a fundamental confessional document of Lutheranism, was not accepted by the emperor and the Catholic estates (see also Confutatio Augustana). In order to prevent a possible military recatholicization of Protestant territories, the Protestant imperial estates then founded the Schmalkaldic League on February 27, 1531. In the following years, several religious discussions took place in order to restore the unity of the church. When these failed - also due to political motives - Emperor Charles V decided to take military action against the League and defeated it in the Schmalkaldic War in 1547.
At the "harnessed" Augsburg Diet of 1548 (so called because Charles's troops were still in the empire), the emperor attempted to use his military victory at Mühlberg politically as well: He forced the Protestant imperial estates to accept the Augsburg Interim. The Interim was intended to regulate ecclesiastical conditions until a general council would finally decide on the reintegration of Protestants into the Catholic Church. However, the largely pro-Catholic provisions issued by Charles were not enforced, or were only half-heartedly enforced, except within the direct reach of imperial power in the south of the empire and in the imperial cities.
At the same time, the question arose as to who should succeed Charles V in the empire. This problem also contributed to the intensification of the existing conflict between the Estates and the Emperor: The emperor himself tried to push through his plan of the so-called Spanish succession, that is, the transfer of the Roman-German imperial dignity to his son Philip II of Spain during his lifetime, in the empire. His brother Ferdinand I, on the other hand, who had already been elected Roman king in 1531, wanted to claim the imperial crown for himself and his descendants. The majority of the imperial estates were more inclined to Ferdinand's position in this matter. They feared that a successor from the Spanish line would be a first step towards a hereditary, Habsburg universal monarchy. In addition, this would at the same time considerably limit their Teutonic liberties, their estates' freedoms.
Moritz of Saxony, despite his Protestant faith, had supported the Emperor in the Schmalkaldic War and received the Saxon electorship for this in 1547. Afterwards, Moritz found himself in a difficult position: he was isolated within the Protestant camp, but was aware that the Emperor's strong position could not last. Therefore, he placed himself at the head of a rebellion of princes rebelling against the Spanish Succession. Because of this change of sides, Moritz was called Judas of Meissen by Catholics and the savior of the Reformation by Protestants. The ensuing war between princes caught Charles completely off guard in 1552 and forced him to flee. The Emperor was not present at the negotiations held in Passau to settle the conflict. Ferdinand I acted as mediator and negotiated with the princes.
In general, the longing for peace gradually arose in the Empire after the numerous unrest and confessional wars of the Reformation period. The War of the Princes was immediately followed by the Second Margravial War (1552-1555), triggered by the territorial claims of Albrecht Alcibiades, Margrave of Brandenburg-Kulmbach. The military and political stalemate between Lutherans and Catholics reduced the hope of being able to further expand one's own sphere of influence. This favored peace inclinations - both sides were willing to make concessions for a comprehensive peace settlement.
Ferdinand I, brother of the reigning Emperor Charles V, had probably come to the realization through the Schmalkaldic War and the subsequent rebellion of the princes that Protestantism could not be defeated by military means. He then convened a Diet in Passau in 1552 to negotiate the relationship between the two confessions with princes and estates of a generation that was now comparatively willing to compromise. The resulting Treaty of Passau, whose provisions were limited in time, was, however, merely a "transitional solution" to religious policy, a "truce". The reason for this was Charles' refusal to sign a treaty that made permanent concessions to the Protestants. Nevertheless, the Treaty of Passau was a step towards a lasting peace, which was to be concluded three years later in Augsburg.
After the Treaty of Passau, Charles V realized that his lofty political goals in the Empire had largely failed and slowly initiated his resignation. He moved to Brussels in 1553 and did not return to the Empire for the rest of his life. He placed imperial politics almost entirely in Ferdinand's hands.