France started the Franco-Prussian War (1870–71), and was defeated by the Kingdom of Prussia and other German states. The end of the war led to the unification of Germany. Otto von Bismarck annexed Alsace and northern Lorraine to the new German Empire in 1871; unlike other members states of the German federation, which had governments of their own, the new Imperial territory of Alsace-Lorraine was under the sole authority of the Kaiser, administered directly by the imperial government in Berlin. Between 100,000 and 130,000 Alsatians (of a total population of about a million and a half) chose to remain French citizens and leave Reichsland Elsaß-Lothringen, many of them resettling in French Algeria as Pieds-Noirs. Only in 1911 was Alsace-Lorraine granted some measure of autonomy, which was manifested also in a flag and an anthem (Elsässisches Fahnenlied). In 1913, however, the Saverne Affair (French: Incident de Saverne) showed the limits of this new tolerance of the Alsatian identity.

Which country defeated the French in 1871?