Cause for Applause Lyrics Follow

The causes of the Franco-Prussian War are deeply rooted in the events surrounding the German unification. In the aftermath of the Austro-Prussian War (1866), Prussia had annexed numerous territories and formed the North German Confederation. Prussia then turned its attention towards the south of Germany, where it sought to expand its influence.
France was strongly opposed to the annexation of the Southern German States (Bavaria, Wurttemberg, Baden and Hesse), which would have created too powerful a country next to its border. In Prussia, a war against France was deemed necessary to arouse German nationalism in those States that would allow the unification of a great German empire. This aim was epitomized by Prussian Chancellor Otto von Bismarck's quote: "I knew that a Franco-Prussian War must take place before a united Germany was formed." Bismarck also knew that France should be the aggressor in the conflict to bring the Southern German States to side with Prussia, hence giving Germans numerical superiority.
The immediate cause of the war resided in the candidacy of a Prussian prince to the throne of Spain –– France feared encirclement by an alliance between Prussia and Spain. The Hohenzollern prince's candidacy was withdrawn under French diplomatic pressure, but Otto von Bismarck goaded the French into declaring war by altering a telegram sent by William I. Releasing the Ems Telegram to the public, Bismarck made it sound as if the king had treated the French envoy in a demeaning fashion. Six days later, France declared war on Prussia and Southern German States immediately sided with Prussia.
French Emperor Napoleon III and Prime Minister Émile Ollivier's eagerness to relieve France from internal political convulsions also contributed to France's declaration of war on Prussia.

Source: Wikipedia