The Franco-Prussian War, often referred to in France as the War of 1870 (19 July 1870 - 10 May 1871) or in Germany as 70/71, was a conflict between the Second French Empire of Napoleon III and the German states of the North German Confederation led by the Kingdom of Prussia. The conflict was caused by Prussian ambitions to extend German unification and French fears of the shift in the European balance of power that would result if the Prussians succeeded. Some historians argue that the Prussian chancellor Otto von Bismarck deliberately provoked a French attack in order to draw the independent southern German states-Baden, Württemberg, Bavaria and Hesse-Darmstadt-into an alliance with the North German Confederation dominated by Prussia, while others contend that Bismarck did not plan anything and merely exploited the circumstances as they unfolded. None, however, dispute the fact that von Bismarck must have recognized the potential for new German alliances, given the situation as a whole. On 16 July 1870, the French parliament voted to declare war on the German Kingdom of Prussia and hostilities began three days later. The German coalition mobilised its troops much more quickly than the French and rapidly invaded northeastern France. The German forces were superior in numbers, had better training and leadership and made more effective use of modern technology, particularly railroads 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 Napoleon III captured and the army of the Second Empire decisively defeated. A Government of National Defence declared the Third Republic in Paris on 4 September and continued the war for another five months; the German forces fought and defeated new French armies in northern France. Following the Siege of Paris, the capital fell on 28 January 1871, and then a revolutionary uprising called the Paris Commune seized power in the capital 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, finally uniting Germany as a nation-state. 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 Otto von 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. The causes of the Franco-Prussian War are deeply rooted in the events surrounding the unification of Germany. In the aftermath of the Austro-Prussian War of 1866, Prussia had annexed numerous territories and formed the North German Confederation. This new power destabilized the European balance of power established by the Congress of Vienna in 1815 after the Napoleonic Wars. Napoleon III, then the emperor of France, demanded compensations in Belgium and on the left bank of the Rhine to secure France's strategic position, which the Prussian chancellor, Otto von Bismarck, flatly refused.[11] Prussia then turned its attention towards the south of Germany, where it sought to incorporate the southern German kingdoms, Bavaria, Württemberg, Baden and Hesse-Darmstadt, into a unified Prussia-dominated Germany. France was strongly opposed to any further alliance of German states, which would have significantly strengthened the Prussian military.