 Pius XII lobbied world leaders to prevent the outbreak of World War II and then expressed his dismay that war had come in his October 1939 Summi Pontificatus encyclical . He followed a strict public policy of Vatican neutrality for the duration of the conflict mirroring that of Pope Benedict XV during World War I , but preached against selfish nationalism and , through the use of diplomacy , sermons and radio broadcasts and the creation of the Vatican Information Service , Pius worked to ameliorate the suffering of the victims of the war . He permitted local churches to assess and formulate responses to the Nazis , and instructed them to provide discreet aid to Jews . 
