Prussian chancellor Otto von Bismarck has contrived to use the issue of the Spanish succession, in which a Hohenzollern prince is a candidate, to provoke France into a belligerent act that will frighten the holdout south German states into joining the Prussian alliance.

The Prussian king had composed a July 13 message to Napoleon III reporting a relatively uneventful meeting with the French ambassador, but Bismarck has edited this so-called Ems telegram to suggest that the meeting had essentially been an exchange of insults.

The French government must therefore either accept a perceived diplomatic defeat or declare war.

Adolphe Thiers, who had been arrested during the December 1851 coup d'état and sent to Mazas Prison, before being escorted out of France, had been allowed to return in the following summer.

His history for the next decade is almost a blank, his time being occupied for the most part on The Consulate and the Empire.

It was only in 1863 that he had reentered political life, being elected by a Parisian constituency.

For the ensuing seven years, he has been the chief speaker among the small group of anti-Imperialists in the French chamber of deputies and is regarded generally as the most formidable enemy of the Empire.

He has made repeated attempts to warn Napoleon III of the Prussian threat, and continues his thus-far fruitless efforts to conclude mutual-defense agreements with other European countries.

While protesting against its foreign enterprises, he has also harped on French loss of prestige, and so helps contribute to stir up the fatal spirit which brings on the war of 1870.

The ongoing Cuban revolt makes great demands on Spain in men (one hundred thousand by 1870) and money.

Isabella II had abdicated her rights in Alfonso's favorI in June 1870.

Juan Prim’s attempts to establish a liberal constitutional monarchy in Spain are compounded by the difficulty in finding a new king.

The consideration, supported by Prim, of Prussia's candidate, Prince Leopold of Hohenzollern-Sigmaringen, is opposed by France.

Prim and the Prussian chancellor, Otto von Bismarck, persuade the reluctant Leopold to accept the Spanish throne.

This move greatly alarms France, who feels threatened by a possible combination of Prussia and Spain directed against it.

Leopold's candidacy is withdrawn under French diplomatic pressure, but the Prussian king William I is unwilling to bow to the French ambassador's demands that he promise to never again allow Leopold to be a candidate for the Spanish throne.

Bismarck edits William's telegraphed description of this interview, and on July 14, he publishes this provocative message, which accomplishes his purposes of infuriating the French government and provoking it into a declaration of war in July.

Napoleon III’s government, mindful of domestic unrest, chooses war over what is seen as the more dangerous course of acknowledging a diplomatic trouncing.

On July 19, Napoleon III declares war on Prussia to prevent German unification, and thereby makes it a war of German national defense.

Léon Gambetta, now war minister, opposes the declaration of war.

Two German armies besiege Paris on September 19.