Among his diplomatic achievements was the signing of a Concordat with Serbia barely four days before the assassination of the Austrian Heir-Apparent Franz Ferdinand in Sarajevo on 28 June 1914 plunged Europe into the First World War. Merry del Val recorded that the "breakthrough" in the difficult negotiations with Belgrade came on the Feast of the Sacred Heart. The Pope and his Cardinal Secretary of State were fully aware that war was imminent. Pius X had already warned a departing Brazilian Ambassador a year earlier that Europe would not "get through 1914" without a major conflagration. Merry del Val remained Secretary of State throughout the pontificate of Pius X, but when Pope Benedict XV, an old associate of Rampolla, was elected in the conclave of 1914, Merry del Val was not reappointed. Benedict XV in fact appointed as his Cardinal Secretary of State, first Domenico Ferrata, who died almost immediately, and then Pietro Gasparri. Thus at the head of the Church were the two bishops – Della Chiesa (now Pope Benedict XV) and Gasparri – who had been leapfrogged by Merry del Val on the eve of the conclave in 1903. However, Benedict XV appointed Merry del Val as secretary of the Supreme Sacred Congregation of the Holy Office on 14 October 1914.