The event directly precipitating the Franco-Prussian War was the candidacy of Leopold, prince of Hohenzollern-Sigmaringen, for the throne of Spain, rendered vacant by the Spanish revolution of 1868. Leopold had accepted the candidacy under persuasion from Bismarck. The French government, alarmed at the possibility of a Prusso-Spanish alliance resulting from the occupancy of the Spanish throne by a member of the Hohenzollern dynastic family, threatened Prussia with war if Leopold's candidacy was not withdrawn. The French ambassador to the Prussian court, Comte Vincente Benedetti, was dispatched to Ems, a spa in northwestern Germany being visited by William I, king of Prussia. Benedetti had been instructed to demand that the Prussian monarch order Prince Leopold to withdraw his candidacy. William, although angered, gave Benedetti permission to communicate directly with Leopold by telegraph. Leopold could not be reached, but his father, Prince Charles Anthony, wired a retraction of the candidacy in the name of his son. The government of Napoleon III, still not content, was determined to humiliate Prussia, even at the cost of war. Antoine Agénor Alfred, duc de Gramont, the French foreign minister, demanded that William submit a personal letter of apology to Napoleon III and a guarantee that the Hohenzollern candidacy would never be renewed. In an interview with Benedetti at Ems, the Prussian king rejected the French demands.The same day,Bismarck obtained William's authorization to publish the French demands and the Prussian rejection contained in what was known as the Ems Dispatch. Bismarck edited the document in a manner calculated to aggravate the resentment of the French and the Germans. The Prussian statesman realized that this move would in all probability precipitate war, but he knew that Prussia was prepared, and he counted on the psychological effect of a French declaration of war to rally the south German states to Prussia's cause, thus accomplishing the final phase in the unification of Germany. On July 19, 1870, France declared war on Prussia. The south German states, in fulfillment of their treaties with Prussia, immediately joined King William in a common front against France.