In the early 1860's, a conflict about army reforms caused a constitutional crisis in Prussia. The Prussian king, Wilhelm I, appointed Otto von Bismarck prime minister in 1862. Bismarck hoped he could resolve the constitutional crisis with foreign triumphs. He also wanted to establish Prussia as the leading German power.

Between 1864 and 1870, Bismarck had the German states fight three short, victorious wars. In the first, Austria and Prussia, in the name of the German Confederation, took the duchies of Schleswig and Holstein from Denmark. In 1866, Bismarck picked a quarrel with Austria. His army easily defeated Austria at Koniggratz in what was called the Seven Weeks' War. Bismarck then dissolved the German Confederation, annexed some territory to Prussia, and established the North German Confederation under Prussian leadership. The four German states south of the Main River remained independent, but made military alliances with Prussia. Austria's defeat left it greatly weakened. In 1867, the Austrian emperor was forced to give equal status to his Hungarian holdings, creating the Dual Monarchy of Austria-Hungary. Austria was never again a power in Germany.

To complete the unification of Germany, Bismarck knew that he needed to overcome the opposition of France. In 1870, he encouraged a Hohenzollern prince to accept the throne of Spain. As Bismarck expected, France objected. Although the prince withdrew as a candidate, Bismarck used the dispute to start the Franco-Prussian War. This conflict pitted France against the North German Confederation and its south German allies. After several battles, the Germans defeated the main French armies at Sedan in September 1870. The German army captured Paris in January 1871. Under the peace treaty, France gave up almost all of Alsace and part of Lorraine.

During the Franco-Prussian War, the four south German states agreed to join a united German nation under Prussian leadership. On Jan. 18, 1871, Wilhelm I was crowned the first kaiser (emperor) of the new German Empire. Wilhelm appointed Bismarck chancellor and head of government.