The Franco-Prussian War was an armed confrontation between Prussia and France in the second half of the 19th century. It took place from July 1870 to May 1871, in France. Backed by the German Confederation, Prussia obtained the victory, which paved the way for the unification of the German states and Prussia, becoming an European super power: the German Empire, ruled by William I, Hohenzollern.
The cause of the war was the possible ascension of a candidate from Prussia’s Hohenzollern House to the Spanish throne, which was opposed by France on the grounds that it would mean the rise of Prussia’s hegemony over Europe. The French government had sent an ultimatum to the King of Prussia, William I, to withdraw the candidacy; to avoid an eminent military conflict, the Prussian king accepted the French demand and withdrew it. In order to humiliate Prussia, the French Emperor, Napoleon III (Louis Napoleon), demanded William I to renounce any possible further Hohenzollern candidature to the Spanish throne. The Prussian king refused as his Prime Minister Otto von Bismarck handed over the French second ultimatum to the press. As a result, the French declared war on Prussia.
The Franco-Prussian War was a six-month military campaign, in which the Prussian-German forces defeated the French in a series of battles fought across northern France. The most important military engagement of the conflict was the Battle of Sedan, on September 1, 1870, in which Napoleon III was captured and forced to abdicate. As a result, a revolt broke out in Paris at the beginning of 1871 and the French Third Republic was declared. However, the war raged on. While Paris was being besieged by the Prussian Army, the German states proclaimed their union under the King of Prussia as William I was declared Emperor of the German Empire in the Hall of Mirrors, Versailles, on January 18, 1871. Paris finally fell on January 28, 1871. Not only did the German states and Prussia became united, but they also recovered the Alsace and the Lorraine, two German regions which had been taken away from Germany at the end of the Thirty Years War.