The Franco-Prussian War or Franco-German War, often referred to in France as the War of 1870, was a conflict between the Second French Empire (and later, the Third French Republic) and the German states of the North German Confederation led by the Kingdom of Prussia.
Lasting from 19 July 1870 to 28 January 1871, the conflict was caused primarily by France’s determination to restore its dominant position in continental Europe, which it had lost following Prussia’s crushing victory over Austria in 1866.
According to some historians, Prussian chancellor Otto von Bismarck deliberately provoked the French into declaring war on Prussia in order to draw four independent southern German states – Baden, Württemberg, Bavaria and Hesse-Darmstadt – into an alliance with the North German Confederation dominated by Prussia. Some historians contend that Bismarck exploited the circumstances as they unfolded. None, however, dispute the fact that Bismarck must have recognised the potential for new German alliances, given the situation as a whole.
France mobilised its army on 15 July 1870, leading the North German Confederation to respond with its own mobilisation later that day. On 16 July 1870, the French parliament voted to declare war on Prussia, and the declaration of war was delivered to Prussia three days later. French forces invaded German territory on 02 August. The German coalition mobilised its troops much more effectively than the French and invaded northeastern France on 04 August. The German forces were superior in numbers, had better training and leadership and made more effective use of modern technology, particularly railways and artillery.
A series of swift Prussian and German victories in eastern France, culminating in the Siege of Metz and the Battle of Sedan, saw French Emperor Napoleon III captured and the army of the Second Empire decisively defeated. A Government of National Defence declared the Third French Republic in Paris on 04 September and continued the war for another five months; the German forces fought and defeated new French armies in northern France. The French capital, Paris, was besieged and fell on 28 January 1871, after which a revolutionary uprising called the Paris Commune seized power in the city and held it for two months, until it was bloodily suppressed by the regular French army at the end of May 1871.
The German states proclaimed their union as the German Empire under the Prussian king Wilhelm I and Chancellor Bismarck. They finally united most of Germany as a nation-state (Austria was excluded). The Treaty of Frankfurt of 10 May 1871 gave Germany most of Alsace and some parts of Lorraine, which became the Imperial territory of Alsace-Lorraine (Reichsland Elsaß-Lothringen).
The German conquest of France and the unification of Germany upset the European balance of power that had existed since the Congress of Vienna in 1815, and Bismarck maintained great authority in international affairs for two decades.
French determination to regain Alsace-Lorraine and fear of another Franco-German war, along with British apprehension about the balance of power, became factors in the causes of World War I.