also called the Austro-Prussian War, military conflict (1866) between Austria and Prussia that left Prussia the dominant power in Germany.

The war was provoked by the Prussian foreign minister Otto von Bismarck. In the 39-state German Confederation, established by the Congress of Vienna in 1815, Prussia and Austria were rivals for leadership, and Bismarck was determined to tip the scales in Prussia's favor. Two years earlier (1864), Austria and Prussia together had made war on Denmark and taken from it the duchies of Schleswig and Holstein. By the Convention of Gastein (1865) Austria had received jurisdiction over Holstein and Prussia over Schleswig and the duchy of Lauenburg. Neither Austria nor Prussia, however, was satisfied with the settlement. Making use of this situation to further his goal, Bismarck interfered in the Austrian administration of Holstein, and when Austria protested to the diet (legislature) of the confederation, he sent Prussian troops into Holstein. Hannover, Hesse-Kassel, Saxony, Bavaria, Württemberg, and some other German states, fearing Prussian expansion, supported Austria. Prussia had secured the neutrality of most non-German powers and concluded an alliance with Italy.

In the actual war, declared by Austria on June 14, the Prussians soon gained the advantage, thanks to their strategist, Count Helmuth von Moltke. They quickly captured Hannover and Hesse-Kassel, then invaded Saxony and Bohemia, and finally inflicted a crushing defeat on the Austrians at Königgrätz in Austria (now Hradec Králové, Czech Republic) on July 3.

By the Treaty of Prague (Aug. 23, 1866) and related agreements, the German Confederation was dissolved; Prussia annexed Hannover and Hesse-Kassel; Austria ceded Holstein to Prussia, paid a small indemnity, and ceded Venetia to Italy. The following year Prussia organized the North German Confederation, from which Austria was excluded, while Austria gathered its remaining territories in the Austro-Hungarian Empire.