The Franco-Prussian War began with a declaration of war by the French emperor, Napoleon III.
The Franco-Prussian War marked the culmination of a long period of declining relations between France and the German state of Prussia. Prussia had defeated Austria in the Seven Weeks’ War three years previously, and France was concerned that the established balance of power within Europe was at risk.
In June 1870 Prince Leopold of Hohenzollern-Sigmaringen, a relative of King Wilhelm I of Prussia, was offered the vacant Spanish throne. Leopold accepted the offer, but Napoleon III complained that the appointment would mean France was surrounded by Prussian influence. In the face of France’s hostility, Wilhelm I persuaded Leopold to withdraw his candidacy.
Count Benedetti, the French Ambassador to Prussia, met Wilhelm shortly afterwards to demand a promise that the candidature would not be renewed. Wilhelm saw this as questioning his honour as a King, and refused to give the promise. He informed Bismarck of the meeting by telegram, and on 14 July the minister released an edited version – known as the Ems Telegram – in which he changed the tone of the conversation to give the impression that Wilhelm had offended the French Ambassador.
This pushed Napoleon, persuaded by the media and his wife, to declare war on Prussia on 19 July 1870. Prussia quickly secured the support of the South German states and, aided by superior military planning and rail links, mobilised quickly. France was defeated decisively within 4 weeks, and Emperor Napoleon III himself was taken prisoner. Although the Siege of Paris prolonged the conflict, the French government signed the Peace of Frankfurt in 1871.