Why did the Protestant Reformation contribute to the decline of Crusading?

The Protestant Reformation contributed significantly to the decline of the Crusades during the 16th century by undermining the theological and institutional foundations that supported them.12

The decline was driven by several key factors:

• Rejection of Indulgences: The doctrine of indulgence—which was central to the Crusading movement as a means for participants to seek redemption and the expiation of sins—was explicitly rejected by Martin Luther and other Protestant reformers.12
• Critique of Papal Authority: Protestants viewed the Crusades as cynical ploys used by the papacy to consolidate power and exert control over secular lords. By challenging the authority of the pope, reformers dismantled the primary mechanism for organizing and legitimizing these military expeditions.13
• Shift in Religious Focus: The Reformation redirected the focus of Western Christianity away from the medieval structures of Christendom, which had previously unified European powers under the banner of holy war.14

While the popes continued to call for Crusades to defend Europe against the Ottoman Turks, the fragmentation of religious and political authority caused by the Reformation meant these calls no longer commanded the same universal support across Europe.12