Introduction
The years 1529 to 1530 marked a decisive moment in the German Reformation, as Imperial politics, Lutheran expansion, and conflicting religious loyalties reshaped the Holy Roman Empire.

Imperial Diets and the Situation in 1529

The Role of Imperial Diets

The Imperial Diet was the representative assembly of the Holy Roman Empire, bringing together princes, electors, and representatives of free cities to deliberate on political and religious matters. These meetings became central arenas for debating and managing the escalating conflict between supporters of Lutheranism and defenders of traditional Catholic orthodoxy.

By 1529, Charles V’s empire faced mounting internal division. The Emperor, heavily preoccupied with wars against France and the Ottoman Empire, delegated authority within Germany to local princes and church leaders. This made the decisions at the Diets crucial in determining the immediate religious trajectory of the Empire.

The Diet of Speyer (1529)

The Second Diet of Speyer represented a turning point. At the earlier Diet of Speyer (1526), princes had been permitted relative freedom in religious practice until a General Council of the Church could decide definitively. However, in 1529, this tolerance was revoked, reaffirming the Edict of Worms (1521), which had outlawed Luther’s teachings. This reversal created immense tension.

• Lutheran princes and cities, including Philip of Hesse and the rulers of Nuremberg and Augsburg, objected strongly.

• Their formal protest against imperial decrees gave rise to the term “Protestant”, which from this point onward defined those opposing Catholic authority in favour of reformed religious practices.

• Charles V, although not present, authorised his representatives to reinforce Catholic orthodoxy, deepening divisions.

Key Figures in 1529

• Philip of Hesse: A committed supporter of Luther, politically ambitious, and instrumental in creating alliances between Protestant princes.

• Frederick the Wise: Though deceased by 1525, his earlier protection of Luther had already laid the groundwork for the persistence of Lutheran thought in Saxony.

• Urban centres like Augsburg and Nuremberg: These cities embraced Lutheran reforms, driven by urban elites and guilds who saw social and economic benefits in curtailing ecclesiastical privileges.

The 1529 situation thus sharpened the divide within the Empire, forcing princes and cities to adopt clearer positions on religion.

The Spread of Lutheranism 1530–1555

The Diet of Augsburg (1530)

At the Diet of Augsburg, Charles V sought religious unity to strengthen imperial authority in the face of external threats. Lutheran leaders, guided by Philip Melanchthon, presented the Augsburg Confession.

Engraved depiction of the presentation of the Augsburg Confession before Charles V at the Diet of Augsburg (25 June 1530). The emperor is shown enthroned, with the estates assembled in a grand hall. As an 18th-century engraving, this is a later visualisation of the historic event. Source

Despite attempts at moderation, the confession was rejected, and Lutheranism was formally outlawed. However, this rejection only consolidated Protestant unity and determination.

Protestant Alliances and the Schmalkaldic League

To defend their religious and political independence, Protestant princes and cities formed the Schmalkaldic League in 1531. This alliance was spearheaded by Philip of Hesse and John Frederick of Saxony. It provided military backing to Lutheranism, making it more than a theological movement—it was now a political and military force.

Key features of the Schmalkaldic League:

• Mutual military defence against imperial or papal attempts at suppression.

• A shared commitment to Lutheran doctrine.

• Significant urban support, especially from trading cities like Nuremberg.

This league enabled Lutheranism to survive and expand despite opposition from the Emperor and the Catholic Church.

The Expansion of Lutheranism

Between 1530 and 1555, Lutheranism spread widely due to several interconnected factors:

• Urban adoption: Cities such as Augsburg and Nuremberg became strongholds, where civic leaders embraced reform to assert independence from clerical authority.

• Noble patronage: Princes like Philip of Hesse used their political power to protect Lutheran preachers and implement reforms.

• Printing press: The wide circulation of Lutheran texts ensured doctrinal consistency and popular engagement.

• Weak imperial enforcement: Charles V’s preoccupation with France and the Ottomans meant limited capacity to suppress reformist regions.

The Schmalkaldic War (1546–1547)

Charles V, alarmed at Protestant strength, eventually waged war against the Schmalkaldic League.

Schmalkaldic War, 1546–1547: a labelled map of Saxony and surrounding regions showing the theatres of conflict, including the Elbe near Mühlberg. Derived from the Cambridge Modern History Atlas (1912). Source

Initially successful at the Battle of Mühlberg (1547), Charles imposed the Augsburg Interim (1548), a temporary religious settlement that attempted to reintegrate Protestants into Catholic practices. However, it faced widespread resistance and failed to resolve religious divisions.

The Peace of Augsburg (1555)

The stalemate culminated in the Peace of Augsburg, a landmark settlement that institutionalised religious division within the Empire.

This agreement legitimised Lutheranism, ensured its survival, and marked the end of Charles V’s dream of religious unity in Germany.

Conclusion of the Period

By 1529 the Empire was irreversibly split, and between 1530 and 1555 Lutheranism spread through alliances, cities, and determined resistance. Imperial Diets both reflected and reinforced this division, while external conflicts prevented Charles V from suppressing reform. Ultimately, Lutheranism became a permanent feature of the German political and religious landscape.