This chapter suggests that the papacy dealt with Protestantism in various ways. It condemned the forty-one propositions of Martin Luther and then waited for the Council of Trent to condemn others. It used the institutions of preventive press censorship and of various inquisitions to check heresy. It sought the support of Christian rulers to prevent its spread, sending nuncios and legates to the rulers of the Holy Roman Empire, France, England, Scotland, Sweden, Denmark, and Poland–Lithuania to urge them to suppress heresy and to secure their loyalty by negotiating agreements on Church appointments and shared revenues and by offering military aid, efforts that had mixed success, or failed. Religious orders such as the Jesuits and Capuchins were also enlisted in the struggle. Leading Protestant reformers came to see the papacy as the Antichrist or foreign usurper.

This chapter examines the brief but formative pontificate of Benedict XV, the most important in the early twentieth-century history of the papacy: Benedict’s return to the policies of Leo XIII (r. 1878–1903) and, above all, his responses to the challenges of the First World War and its aftermath, transformed the scope and impact of Vatican diplomacy, restoring its prestige and influence on the international stage. More broadly speaking, Benedict set the agenda of the next two pontificates, those of his successor Pius XI (r. 1922–39) and Pius XII (r. 1939–58). They continued the policy of seeking to implement the new Code of Canon Law, and where possible by concordats with states, they would continue to seek reunion with the Orthodox Churches and Benedict’s postcolonial vision for the missionary outreach of the Church. They would also continue to follow the broad outlines of his initiatives in Vatican diplomacy through his commitment to seeking to play a role in international peace and security. Benedict’s policy of impartiality in war was not a passive one, but active and constructive, aimed both at providing humanitarian relief to victims and encouraging peace negotiations between the belligerents. His peace-making and humanitarian efforts reflected new forms of papal humanitarian diplomacy and have become a permanent feature of the papacy’s role in promoting international peace and security.