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The War of 1866 and the Undoing of Vienna

By: Randall Lesaffer

On 3 July 1866, the Austrian and Prussian armies engaged each other near Königgrätz and Sadowa in Bohemia. Although the commanders of both forces had not planned for such a clash that day, what followed was one of the greater pitched battles of the mid-19th century.  At the end of the day, the Austrian army had to withdraw, leaving 40,000 casualties. The battle as good as ended the war, which had begun only a few weeks before. The Austrian Empire was militarily speaking a spent force and could not hope to continue the war and survive. Its German allies had collapsed or were on the verge of doing so, its treasury was empty, and political unrest among the many nations which made up the Habsburg Empire spelled doom if the war against Prussia and Italy went on. Less than three weeks later, the Austrian Emperor Franz Joseph (r. 1848–1916) sued for peace. On 26 July, the two powers signed a preliminary peace at Nikolsburg (132 CTS 463), followed by the Peace of Prague on 23 August (133 CTS 71).

Prussia imposed a harsh victor’s peace on Austria. The Habsburg Empire had to cede Venice to Italy (Art. 1), leave Holstein to Prussia (Art. 5), and pay Prussia a huge indemnity of 40,000,000 thalers for its war costs (Art. 11). But most importantly, the peace ended Austria’s role within the German political sphere. It had to relinquish Germany to Prussian hegemony. Austria was forced to accept the dissolution of the German Confederation (Art. 4), the successor of the Holy Roman Empire which the Austrian Habsburgs had headed for over three centuries and which was still the vehicle of its influence. It also had to recognize Prussia’s arrangements in the north, including the formation of a Northern German Confederation and eventually even a Southern one, both of which would be dominated by Berlin. To top it all, Austria promised to recognize any territorial rearrangements Prussia imposed upon the German states, most of which had been allies of Austria during the war. Only for its staunchest ally Saxony could Austria obtain a limited reservation (Art. 6).

With this, the Peace of Prague undid the settlement which the Congress of Vienna (1814–1815) had made for Germany at the end of the Napoleonic Wars, and which was the geopolitical linchpin of the Vienna system. At Vienna, the victorious great powers had most of all tried to restore and secure the balance of power. To achieve this, they needed to contain France by surrounding it with powerful states. The greatest riddle to solve this puzzle was Germany. Whereas it was not an option to return to the extreme division of the defunct Holy Roman Empire with over 300 estates and 1,500 imperial fiefs, neither could the unification of Germany, albeit passionately desired by many among the German elite, be contemplated. Not only was such a move unimaginable because it clashed with the principle of dynastic legitimacy on which the Vienna system was also founded, but moreover it would create a power in the centre of Europe which could not be contained. The solution was found in a duopoly of Austria and Prussia which would form a bulwark against France to the west and create a balance of power within Germany. This solution was facilitated by Napoleon’s (1769–1821) rearrangement of Germany from 1806, which had led to the abolition of the old Empire and the drastic reduction of the number of estates and dynasties to be taken into consideration.

The result was a patchwork of 39 German states, which were loosely joined together in the German Confederation (Deutscher Bund) under the presidency of Austria (Act Relative to the Federal Constitution of Germany, signed at Vienna, 8 June 1815, 64 CTS 443), in which both Austria and Prussia saw their territories extended, and Austria obtained large parts of Northern Italy as a check on French ambitions on the peninsula, whereas Prussia was granted much of the Northern Rhineland and Westphalia to oppose French expansionism there. The Vienna system was further secured by an alliance between Austria, Prussia, and Russia.

The Vienna Congress left Prussia largely dissatisfied. It would have preferred to swallow up the Kingdom of Saxony and thus consolidate its power around its heartlands, rather than to be pitched against France. Furthermore, the weakness of the German Confederation and the leading role of Austria therein left Prussia exposed to France without being able to count on the rest of Germany. Finally, within the alliance of the three eastern powers, it was the junior partner.

The first great crack in the mould of Vienna came in the early 1850s. During the Crimean War, Austria sided with the Western powers Britain and France, thus ending the alliance of the three eastern powers. This left Austria exposed to its traditional enemy, France, now under the leadership of Emperor Napoleon III (1808–1873). In 1859, a first confrontation followed. In March 1859, Paris signed a secret agreement with Saint Petersburg whereby the Russian government promised to stand aside in case of a war with Austria over Italy. Later that year, France and its ally Piedmont-Sardinia provoked a war with Austria. Prussia at first remained neutral, but after the tide of the war turned against Austria and its collapse threatened, it mobilized its forces to deter France. At the Peace of Zurich of 10 November 1859 (121 CTS 145 and 121 CTS 155), Vienna came away with the cession of Lombardy to Piedmont-Sardinia, but was able to retain Venice.

The Austrian humiliation created greater room for manoeuvre for Prussia both within and without Germany. Long before he became prime minister of Prussia in 1862, Otto von Bismarck (1815–1898) had pleaded for a change of course. According to him, Austria was the main brake on Prussia’s ambition to gain the leadership it craved in Northern Germany, with an eye on harnessing the resources of that area. He thus advocated for a policy that would weaken Austria and allow for a rearrangement of the Vienna settlement.

After his accession to power in 1862, Bismarck saw his first opportunity to further undercut Vienna’s position within the German Confederation with the Schleswig-Holstein crisis at the end of 1863. The crisis, which was caused by Denmark’s annexation of Schleswig, came at a time when the German states were locked in a debate about constitutional reform. This pitted Austria against Prussia. In September 1863, Austria had introduced a proposition that would have strengthened the efficiency of the Confederation but would have left the confederal model – with a Federal Assembly consisting of representatives of the states – and its leadership intact. Prussia opposed the Viennese reform plans as it desired an alternate presidency between the two leading powers.  Bismarck made the bold move of pleading for an assembly which would be elected through general suffrage. Hereby he hoped to make Austria and the German princes do his bidding.

Bismarck’s strategic choice to cooperate with Austria in the Schleswig-Holstein crisis and its outcome need to be assessed against the backdrop of this debate. Lacking the support of the Prussian King Wilhelm I (r. 1861–1888) for a bolder course and fearing the alienation of most other members of the Confederation, to Bismarck cooperation with Vienna was the only context in which he could go to war against Denmark. Moreover, it offered an opportunity to act as joint leader of the Confederation and show the effectiveness of that constellation. The war which ensued was a resounding success for Bismarck. It strengthened his position both within Prussia and with German nationalists. The joint administration of Schleswig-Holstein by Austria and Prussia immediately became a source of constant struggle and tedious negotiations which formed a platform for Bismarck to convince others in Berlin that destroying Austria as a leading German power should be Prussia’s priority.

Through the Convention of Bad Gastein of 14 August 1865 with Austria (131 CTS 343), Prussia gained control over Schleswig as well as the Duchy of Lauenburg, located between Holstein and Prussian territory. This success, however, only served to whet the appetite of a growing part of the Prussian government and military command. Moreover, the time for a war with Austria was propitious as the empire was riddled with nationalist unrest and was very nearly bankrupt. Also, Prussia had good reasons to hope that the other three great powers would stand aside as they had done during the war of 1864.

In early 1866, the Prussian government decided to go to war with Austria. In April 1866, Bismarck secured an alliance with Italy, which promised to attack Austria if war erupted between Austria and Prussia within 90 days. Bismarck had no intentions to let this deadline slip although he still needed a pretext for war. This came in early June when Austria decided to convene an assembly for Holstein. Bismarck interpreted this as a violation of the Convention of Bad Gastein, which in the vaguest of terms had kept the fiction of the unity between Holstein and Schleswig alive. On 10 June, he introduced a new proposal for reform of the German Confederation, including general suffrage. While this strengthened the resolve of German princes to side with Austria, it also undercut their position at home. The same day, the Prussian army sprang into action by invading Holstein. 

Within the space of a month, the war was decided. In spite of some initial difficulties in the north and south-west of Germany and the bad performance of its ally Italy, the Prussian victory was complete. It allowed Bismarck to dictate the peace. The peace settlement Bismarck brokered sealed the end of the Vienna system. In a series of treaties with Austria and the German states, a new settlement for Germany was laid out. Firstly, the German Confederation was abolished. Secondly, a Northern German Confederation was founded. The Northern German states had to agree to the calling of a parliament through general suffrage and had to turn over the supreme command of their armed forces to Berlin (Treaty of Alliance, signed at Berlin, 18 August 1866, 133 CTS 39). Thirdly, Prussia made some major territorial rearrangements, whereby it annexed Schleswig-Holstein, the Kingdom of Hanover, the Electorate of Hesse, the Duchy of Nassau, the Free City of Frankfurt, and the southern parts of the Grand-Duchy of Hesse-Darmstadt (Treaty of Peace between Hesse-Darmstadt and Prussia, signed at Berlin, 3 September 1866, 133 CTS 147). Fourthly, the Southern German states were forced into secret alliance treaties with Prussia whereby they turned over the command of their troops (Treaty with Wurttemberg, signed at Berlin, 13 August 1866, 133 CTS 27; Treaty with Baden, signed at Berlin, 17 August 1866, 133 CTS 37; Treaty with Bavaria, signed at Berlin, 22 August 1866, 133 CTS 53).

With the 1866 peace settlement, Bismarck succeeded in achieving his major foreign policy goals and more. The lock which Vienna had set on Prussia’s ambition in Northern Germany was broken. The result was much better than the previously desired duopoly with Prussia ruling the North and Austria the South, as the settlement excluded Austria altogether from German affairs and left the field to Prussia alone. The road to the unification of all of Germany under Prussian leadership lay wide open.



Christopher Clark, Iron Kingdom. The Rise and Downfall of Prussia, 1600-1947 (London: Allen Lane 2006).

Mark Jarrett, The Congress of Vienna and its Legacy. War and Great Power Diplomacy after Napoleon (London: I.B. Tauris 2014).

Henry Kissinger, Diplomacy (New York: Simon & Schuster 1994).

Paul W. Schroeder, The Transformation of European Politics 1763-1848 (Oxford: Clarendon Press 1994).

Brendan Simms, Europe. The Struggle for Supremacy, 1453 to the Present (London: Allen Lane 2013).

Jonathan Steinberg, Bismarck. A Life (Oxford: Oxford University Press 2011).

A.J.P. Taylor, The Struggle for Mastery in Europe 1848-1918 (Oxford: Clarendon Press 1954).

Brian E. Vick, The Congress of Vienna. Power and Politics after Napoleon (Cambridge, MA, and London: Harvard University Press 2014).

Adam Zamoyski, Rites of Peace. The Fall of Napoleon and the Congress of Vienna (London: Harper Press 2007).