Answer: the correct answer is B. to gain control of the German-speaking provinces of Alsace and Lorraine
Explanation: as a consequence of the war 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.