The Austro-Prussian War (also called the Seven Weeks War) was a war fought between Austria and Prussia in 1866 that resulted in Prussian dominance in Germany. In Germany and Austria it is called Deutsch-Deutscher Krieg or Bruderkrieg (war of brothers)

Causes

For centuries, the Holy Roman Emperors in Austria had nominally ruled all of Germany, but the powerful nobles maintained de facto independence with the assistance of outside powers, particularly France. Prussia had become the most powerful of these states, and by the nineteenth century was considered one of the great powers of Europe. After the Napoleonic Wars ended in 1815, French influence in Germany was weak and nationalist ideals spread across Europe. Many observers saw that conditions were developing for the unification of Germany, and two different ideas of unification developed. One was a Grossdeutschland that would include the multi-national empire of Austria, and the other (preferred by Prussia) was a Kleindeutschland that would exclude Austria and be dominated by Prussia.

Prussian statesman Otto von Bismarck became chancellor of Prussia in 1862, and immediately began a policy focused on uniting Germany as a Kleindeutschland under Prussian rule. Having raised German national consciousness by convincing Austria to join him in the Second war of Schleswig, he then provoked a conflict over the administration of the conquered provinces of Schleswig-Holstein. Austria declared war and called for the armies of the minor German states to join them

Alliances

Most of the German states sided with Austria against Prussia, perceived as the aggressor. These included Saxony, Bavaria, Baden, Württemberg, Hanover, Hesse-Kassel, and Nassau.

Some of the northern German states joined Prussia, in particular Oldenburg, Mecklenburg, and Braunschweig. Also, Italy joined with Prussia, because Austria still occupied the territory of Venetia which Italian irredentists wanted in order to complete Italian unification.

Notably, the other foreign powers abstained from this war. French Emperor Napoleon III, who expected an Austria victory, chose to remain out of the war to strengthen his negotiating position for territory along the Rhine, while Russia still bore a grudge against Austria from the Crimean War.

Course of the War

The main campaign of the war occurred in Bohemia. Prussian Chief of the General Staff Helmuth von Moltke had planned meticulously for the war, and chose to mostly ignore the minor states in favor of a concentration against Austria. He rapidly mobilized the Prussian army and advanced across the border into Saxony and Bohemia, where the Austrian army was concentrating for an invasion of Silesia. There, the Prussian armies led personally by King Wilhelm converged, and the two sides met at the Battle of Königgrätz (Sadowa) on July 3. Superior Prussian organization and élan decided the battle against Austrian numerical superiority, and the victory was near total, with Austrian battle deaths nearly seven times the Prussian figure. Austria rapidly sought peace after this battle.

Except for Saxony, the other German states allied to Austria played little role in the main campaign. Hanover's army defeated Prussia at Langensalza on June 27, but within a few days they were foced to surrender by superior numbers. Prussian armies fought against Bavaria on the Main River, reaching Nuremberg and Frankfurt.

Although the Austrians were more successful in their war with Italy, defeating the Italians on land at the Second Battle of Custozza (June 24) and on sea at the Battle of Lissa (July 20), the Austrian defeat in Central Europe forced the Austrians to make peace, ceding Venetia to the Italians by the Treaty of Vienna (October 12).(Although Austria had already ceded Venetia to France for their neutrality before the war who would have given it to Italy anyway.)

Aftermath

In order to forestall intervention by France or Russia, Bismarck pushed the king to make peace with the Austrians rapidly, rather than continue the war in hopes of further gains. The Austrians accepted mediation from France's Napoleon III. The Treaty of Prague on August 23, 1866 resulted in the dissolution of the German Confederation, Prussian annexation of Schleswig-Holstein, Hanover, Hesse-Kassel, Nassau, and Frankfurt, and the exclusion of Austria from German affairs. This left Prussia free to form the North German Confederation the next year. Prussia chose not to seek Austrian territory for itself, and this made it possible for Prussia and Austria to ally in the future, since Austria was threatened more by Italian and Pan-Slavic irredentism than by Prussia.

The war left Prussia dominant in Germany, and German nationalism would compel the remaining independent states to ally with Prussia in the Franco-Prussian War in 1870, and then to accede to the crowning of King Wilhelm as German Emperor. United Germany would become by far the strongest power in Europe.