The Franco-Prussian War or Franco-German War, often referred to in France as the 1870 War (19 July 1870 – 10 May 1871), is a conflict between France and Prussia, which is backed by the North German Confederation and the South German states of Baden, Württemberg and Bavaria.

The thorough Prussian and German victory brings about the final unification of the German Empire under King William I of Prussia.

It also marks the downfall of Napoleon III and the end of the Second French Empire, which is replaced by the Third Republic.

As part of the settlement, almost all of the territory of Alsace-Lorraine is taken by Prussia to become a part of Germany, which it would retain until the end of the First World War.

The conflict is a culmination of years of tension between the two powers, which had finally come to a head over the issue of a Hohenzollern candidate for the vacant Spanish throne, following the deposition of Isabella II in 1868.The public release of the Ems Dispatch, which plays up alleged insults between the Prussian king and the French ambassador, inflames public opinion on both sides.

France mobilizes, and on July 19 declares war on Prussia only, but the other German states quickly join on Prussia's side.The superiority of the Prussian and German forces is soon evident, due in part to efficient use of railways and innovative Krupp artillery.

A series of swift Prussian and German victories in eastern France culminate in the Battle of Sedan, at which Napoleon III is captured with his whole army on 2 September.

Yet this does not end the war, as the Third Republic is declared in Paris on 4 September 1870, and French resistance continues under the Government of National Defence and later Adolphe Thiers.Over a five-month campaign, the German armies defeat the newly recruited French armies in a series of battles fought across northern France.

Following a prolonged siege, Paris falls on 28 January 1871.

Ten days earlier, the German states had proclaimed their union under the Prussian King, uniting Germany as a nation-state, the German Empire.

The final peace Treaty of Frankfurt is signed 10 May 1871, during the time of the bloody Paris Commune of 1871.