Seven Weeks' War, or Austro-Prussian War (1866), a war between Prussia and Austria, the two most powerful members of the German Confederation. The war was brought on by the determination of Prussian statesman Otto von Bismarck to expel Austria from the confederation, a necessary step in his plan to unify Germany under Prussian leadership.

In 1864 Prussia and Austria as allies in a war against Denmark had gained control of the duchies of Schleswig and Holstein. Though jointly held, Schleswig was administered by Prussia, and Austria governed Holstein. Intent upon annexing both duchies, Bismarck invaded Holstein in 1866, precipitating a war with Austria.

Italy, an ally of Prussia, was quickly defeated in its attempt to seize the province of Venetia. Prussian forces, led by General Hermuth K. B. von Moltke, quickly defeated Hanover, an Austrian ally. The decisive action of the war occurred in Bohemia, where on July 3 the Prussians scored an overwhelming victory against the Austrians at Sadowa near Königgrätz (what is now Hradec Králové, Czech Republic). A truce was signed before the end of the month.

By the Treaty of Prague (August, 1866), Austria agreed to the dissolution of the German Confederation and its replacement by a federation, to be under Prussian domination, of states north of the Main River. Austria also renounced its rights to Schleswig-Holstein and allowed Prussia to annex four German states. Italy received Venetia. The terms of the treaty were considered moderate since Prussia annexed no Austrian territory and demanded no indemnity. This leniency on the part of Bismarck paved the way for Austria's future cooperation with Prussia.