Canon law has played a role in the life of the Church since its earliest days. For many centuries, it was largely customary and local. However, from the sixth century on, the Roman pontiff played an increasingly prominent role in shaping and applying this law in the West. This tendency to centralize authority in the hands of the Roman pontiff reached its culmination with the promulgation of the first Code of Canon Law in 1917. Cut off from the law’s roots in history and theology, this code derived its force from the will of the pontiff who enacted it. The Second Vatican Council, from 1962 to 1965, attempted to balance the role of the pope with that of the College of Bishops and to move toward decentralization of authority by enhancing the figure of the diocesan bishop and creating episcopal conferences. These conciliar efforts have been implemented, at least in part, in the revised Latin code of 1983 and the Code of Canons of the Eastern Churches of 1990. Nevertheless, subsequent legislating has come largely through the unilateral action of the Roman pontiff.

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.