Austro-Prussian War

The Austro-Prussian War (German: Preußisch-Österreichischer Krieg) was fought in 1866 between the Austrian Empire and the Kingdom of Prussia, with each also being aided by various allies within the German Confederation. Prussia had also allied with the Kingdom of Italy, linking this conflict to the Third Independence War of Italian unification. The Austro-Prussian War was part of the wider rivalry between Austria and Prussia, and resulted in Prussian dominance over the German states, having confirmed Prussia's superior military organization and technology compared to Austria at the time.

The major result of the war was a shift in power among the German states away from Austrian and towards Prussian hegemony. It resulted in the abolition of the German Confederation and its partial replacement by the unification of all of the northern German states in the North German Confederation that excluded Austria and the other southern German states, a Kleindeutsches Reich. The war also resulted in the Italian annexations of the Austrian realm of Venetia.

The war erupted as a result of the dispute between Prussia and Austria over the administration of Schleswig-Holstein, which the two of them had conquered from Denmark and agreed to jointly occupy at the end of the Second Schleswig War in 1864. The crisis started on 26 January 1866, when Prussia protested the decision of the Austrian Governor of Holstein to permit the estates of the duchies to call up a united assembly, declaring the Austrian decision a breach of the principle of joint sovereignty. Austria replied on 7 February, asserting that its decision did not infringe on Prussia's rights in the duchies. In March 1866, Austria reinforced its troops along its frontier with Prussia. The Kingdom responded with a partial mobilization of five divisions on 28 March.

The Prussian Minister President Otto von Bismarck made an alliance with Italy on 8 April, committing it to the war if Prussia entered one against Austria within three months, which was an obvious incentive for him to go to war with Austria within three months so that Italy would divert Austrian strength away from Prussia. Vienna responded with a mobilization of the Southern Army on the Italian border on 21 April. Italy called for a general mobilization on 26 April and Austria ordered its own one the next day. Prussia's general mobilization orders were signed in steps on 3, 5, 7, 8, 10 and 12 May.

When Austria brought the Schleswig-Holstein dispute before the German Diet on 1 June and also decided on 5 June to convene the Diet of Holstein on 11 June, Prussia declared that the Gastein Convention of 14 August 1865 had thereby been nullified and invaded Holstein on 9 June. When the German Diet circumvened the creation of a national parliament proposed by the Kingdom and responded by voting for a partial mobilization against Prussia on 14 June, Bismarck claimed that the German Confederation had ended. The Prussian Army invaded Hanover, Saxony and the Electorate of Hesse on 15 June. Italy declared war on Austria on 20 June.

For several centuries, Central Europe was split into a few large- or medium-sized states and hundreds of tiny entities, which while ostensibly being within the Holy Roman Empire ruled by the Holy Roman Emperor, operated in a largely independent fashion. When an existing Emperor died, seven secular and ecclesiastical prince-electors, each of whom ruled at least one of the states, would elect a new Emperor. Over time the Empire became smaller and by 1789 came to consist of primarily German peoples (aside from Bohemia, Moravia, the southern Netherlands and Slovenia). Aside from five years (1740–1745), the Habsburg family, whose domain was Austria, controlled the Emperorship from 1440 to 1806, although it became increasingly ceremonial only as Austria found itself at war at certain times with other states within the Empire, such as Prussia, which in fact defeated Austria during the War of Austrian Succession to seize the province of Silesia in 1742.

While Austria was traditionally considered the leader of the German states, Prussia became increasingly powerful and by the late 18th century was ranked as one of the great powers of Europe. Francis II's abolition of the office of Holy Roman Emperor in 1806 also deprived him of his imperial authority over most of German-speaking Europe, though little true authority remained by that time; he did, however, retain firm control of an extensive multi-ethnic empire (most of it outside the previous boundaries of the Holy Roman Empire). After 1815, the German states were once again reorganized into a loose confederation: the German Confederation, under Austrian leadership. Prussia had been contesting Austria's supremacy in Germany since at least 1850, when a war between the two powers had nearly erupted over Berlin's leadership of the Erfurt Union, though at that time Prussia had backed down.

At the time of the war, there was no strong national consciousness in Germany. Michael Hughes notes that in regards to Germany, "nationalism was a minority movement, deeply divided and with only a marginal impact on German political life". German newspapers were almost exclusively concerned with local affairs or their respective state governments, and the individual German states cultivated loyalty towards themselves. While rivalry with France was an important element of German nationalist myth-making, many Germans cooperated with France during the Napoleonic Era, and those who resisted France did not do so out of nationalist sentiment. According to John Breuilly, any sense of a common German identity "was weakly developed and confined to particular groups" and "there was very little demand, certainly at popular level, for unification". The liberal-nationalist concept of a united Germany had also become unpopular following the fall of the Frankfurt Parliament in 1849. One of the strongest social forces in Germany at the time was religion, which provided Germans with common confessional values and identities that transcended national boundaries. This led to a strong confessional rivalry between the southern Catholic and northern Protestant states. Breuilly remarks that the confessional rivalry was so strong that "a Hamburg Lutheran had more in common with a Swedish Lutheran than with an Austrian Catholic". The minor nations of Germany valued their independence and believed that their ability to remain sovereign depended on Austro-Prussian dualism, with neither side allowed to become too powerful. Confessional division also played an important role in German dualism, and there was a strong pressure in Catholic states to support Austria. In the absence of nationalist sentiment, a united German state could only be created through external force. Bismarck recognised this, remarking in 1862 that a united German state could not be forged through "speeches and majority decisions" but only through "blood and iron".