Pacelli became the under-secretary in 1911, adjunct-secretary in 1912 (a position he received under Pope Pius X and retained under Pope Benedict XV), and secretary of the Department of Extraordinary Ecclesiastical Affairs in February 1914. On 24 June 1914, just four days before Archduke Franz Ferdinand of Austria was assassinated in Sarajevo, Pacelli, together with Cardinal Merry del Val, represented the Vatican when the Serbian Concordat was signed. Serbia's success in the First Balkan War against Turkey in 1912 had increased the number of Catholics within greater Serbia. At this time Serbia, encouraged by Russia, was challenging Austria-Hungary's sphere of influence throughout the Balkans. Pius X died on 20 August 1914. His successor Benedict XV named Gasparri as secretary of state and Gasparri took Pacelli with him into the Secretariat of State, making him undersecretary. During World War I, Pacelli maintained the Vatican's registry of prisoners of war and worked to implement papal relief initiatives. In 1915, he travelled to Vienna to assist Monsignor Raffaele Scapinelli, nuncio to Vienna, in his negotiations with Emperor Franz Joseph I of Austria regarding Italy.