The Seven Weeks' War: How Prussia Defeated Austria and Reshaped Europe

For one great power, it was the military disaster that ended decades of hegemony over the German-speaking world. For the other, it was the victory that catapulted their nation into the diplomatic big leagues. In the summer of 1866, the Seven Weeks’ War saw the Central European powers of Prussia and Austria go toe to toe, slugging it out for supremacy in a fight that was as nasty as it was short.

But while it may have been over quicker than an average school summer vacation, the effects would be felt for decades to come. It was thanks to this one war that Otto von Bismarck was able to begin uniting the German states, paving the way for the rise of Germany; that Italy was able to absorb Venetia, advancing its own battle for unification; and that the great empire known as Austria-Hungary was officially formed. All too often overlooked, semi-forgotten in the shadow of the larger Franco-Prussian War, this is the story of the Seven Weeks’ War, and the summer that changed German history.

The German Confederation and Its Rival Powers

Sprawling over roughly 358,000 km², Germany today is one of Europe’s largest countries, an economic behemoth beating at the continent’s heart. Yet had one opened a map in 1848, there was no single Germanic nation to be found. Instead, Central Europe was carved up into a constellation of statelets and free cities — 39 in total — that together made up something known as the German Confederation.

Created in 1815 from the ashes of the Napoleonic Wars, the German Confederation was intended by the Allies to be a rational replacement for the collapsed Holy Roman Empire. Only, the memo apparently left out the “rational” part. With a dizzying set of voting rules — that included federal representation of non-Germanic states like Britain and Denmark that just happened to have holdings in the area — the Confederation was less a slumbering giant and more a dysfunctional assembly.

This was made worse by the fact that the only two serious powers among the 39 — Prussia and Austria — were bitterest rivals constantly competing for influence. The continent-wide revolutions of 1848 upended the European order. But in the Germanic states, the eruption was especially volcanic.

Riding a wave of nationalism, citizens of the Confederation tried to combine all their statelets together into a united “Germany,” piloted by Prussian king Frederick William IV. The only problem was that Frederick wasn’t remotely interested. For Frederick, the idea of turning in his shiny Prussian crown for some drab, semi-ceremonial role leading a united Germany was even less appealing than the concept of France.

Nor was the other great Germanic power onboard. As a multi-ethnic empire, the only way Austria could join this new Germany would be by voluntarily surrendering its other possessions. With the Hungarians already revolting, the last thing the emperor wanted was an excuse for more nationalities to go rogue.

Bereft of serious support, the United German parliament had collapsed by 1850. Across Europe, most of the revolutions fizzled out. But that doesn’t mean there hadn’t been some big changes.

In Austria, the old emperor had fallen, replaced by the dashing, soon to be extremely bewhiskered Franz Josef. In France, the king had been democratically replaced by Napoleon’s nephew, Louis Napoleon — who would soon not-so-democratically declare himself Emperor Napoleon III. But perhaps the biggest change was in the fortunes of a minor Prussian nobleman.

Otto von Bismarck had been known to Frederick William IV even before the revolutions of 1848. But it had been his steadfast support for the king during the upheavals that brought him into the limelight. And while it would take a few more years before he graduated to headline act, it was his rise more than anything that would soon facilitate the Seven Weeks’ War.

The Humiliation at Olmütz and Bismarck’s Rising Influence

The other big, post-1848 change was the effective collapse of the German Confederation. With the revolutions mostly over, the Confederation would need to be reformed. But it wouldn’t happen on the same terms as before.

In 1850, a new German uprising threatened the Elector of Hesse, who panicked and called in the big guns. Both Prussia and Austria arrived with their armies — only to instead nearly wind up fighting each other. At which point, Austria called in its own big gun: Russia.

With Russia threatening to intervene on Vienna’s behalf, Prussia was forced to back down. A humiliating agreement was reached at Olmütz (today Olomouc in Czech Republic) that effectively reformed the Confederation with Austria now at its head. But while the Punctation at Olmütz was a slap in the face for Prussia, it wasn’t quite the final triumph Franz Josef thought it was.

Because Otto von Bismarck was by now starting to form the vaguest inklings of a plan. A plan that would soon see Berlin’s humiliation reversed a thousand times over. Depending on where one stands on the whole “Bismarck always had a plan” interpretation of history, the next decade-plus can either be read as a series of strategic Austrian blunders that Prussia took advantage of, or the slow unfolding of a methodical plan to bleed the Austrian giant dry.

The bleeding started not long after Prussia’s humiliation, with the 1853 outbreak of the Crimean War. A clash between Russia and the Ottoman Empire that eventually dragged in other Great Powers like France and Britain, the Crimean War was the biggest conflict Europe had seen in decades. It was also a diplomatic nightmare for Austria.

From the outset, Russia kept pressing Vienna to attack the Turks. But because Prussia was leaning the other way towards backing France and Britain, Austria became extremely nervous about leaving itself friendless in Central Europe. So they overcompensated, eventually joining a formal alliance with the Western European powers, and asking the German Confederation for permission to declare war on Russia.

At which point, Prussia executed a flawless diplomatic maneuver. With Vienna now allied with Paris, it was easy for Berlin to sidle up to the minor German states and whisper that declaring war would mean a French army marching over their territory to reach Russia. When the vote came, Austria was defeated.

The German Confederation didn’t declare war. The overall effect on the war’s outcome was minuscule. But it did leave Russia angry that Austria had turned traitor, while also isolating Vienna among the German statelets.

Bismarck’s Rise to Power and the Second Schleswig War

The next cut came courtesy not of Prussia, but of Louis Napoleon. In 1859, the Italians launched their Second War of Independence against Vienna’s holdings in their north. Eager to play the conquering hero, Napoleon III threw France’s weight behind their bid.

Together, the French and Italians defeated Austria in northern Italy, leaving only Venetia under Vienna’s control. The outcome of that war would turn out to be extremely important in Berlin. Chief of Staff Helmuth von Moltke took note of the successful tactics, and immediately began applying them to the Prussian Army — a key part of his drive to professionalize Berlin’s forces.

Bismarck, meanwhile, pushed the idea of an alliance between Prussia and newly-humiliated Austria. One that would soon reap great rewards. But first, Prussia needed to get stronger.

In January 1861, Frederick William IV died and was replaced on the throne by his brother, Wilhelm I. And Wilhelm was a ruler even more receptive to Bismarck than his brother had been. By 1862, he’d promoted him to Minister President — effectively Prussia’s civilian leader.

What followed was a national transformation. This was the era of blood and iron, when Bismarck hammered through plans to improve Prussia’s economy and might, all while Helmuth von Moltke was creating a sleek fighting machine. By 1864, they had something nearly unique in Europe: a vast professional army led not by aristocrats, but by men with impeccable credentials in management and logistics.

Now all they needed was an excuse to test their new forces. It was an excuse Denmark would be only too happy to provide. In this era, Denmark and the German Confederation were constantly bickering over Schleswig and Holstein — two tiny duchies joined in personal union with Denmark.

While their ruler was Danish, both Schleswig and Holstein had German majorities. Majorities that, in the heat of the 1848 revolutions, had risen up against the Danes. Although the Danes had won the First Schleswig War, they hadn’t annexed the duchies outright.

Holstein even remained a member of the German Confederation. In 1863, the childless Danish king died. Because Holstein only allowed direct male-line succession, that should have meant its personal union with Denmark was over.

But instead the new king tried to cling onto Holstein, illegally asserting dominance over a helpless member of the German Confederation. It would be all the casus belli Bismarck needed to both field test Moltke’s new army and inflict on the Austrian giant the deepest cut of all. In January 1864, Bismarck convinced Franz Josef to join his anti-Copenhagen invasion.

The Prussian-Austrian force that hit the Danes that February swept them away. By April, the Danes had been carried out of Schleswig and Holstein, triggering a peace conference. When that failed, the allied forces simply rolled on, washing over Denmark’s mainland before finally depositing the Danes onto the shores of defeat.

The aftermath of the Second Schleswig War removed both duchies from Danish control, handing them jointly to Prussia and Austria.

Diplomatic Isolation of Austria and the Road to War

What followed was a year of bitter haggling over who got what, until, in Summer 1865, it was finally agreed to give Holstein to the Austrians, and Schleswig to the Prussians. Known as the Treaty of Gastein, the agreement further stipulated that no other German states could interfere in the duchies’ running — a clause that would soon become important. Each power received one province, and on the surface, everyone was satisfied.

Except, of course, that wasn’t Bismarck’s plan at all. At the same time Berlin and Vienna were haggling over who got what, Prussia’s Minister President was quietly doing the diplomatic rounds. And he liked what he was hearing.

In St. Petersburg, people were still angry at Vienna for the whole Crimean backstabbing. In London, Austria’s joint attack on Denmark had made them deeply unpopular.

In Paris, Napoleon III was willing to ignore any moves Berlin made against his old enemy Vienna, so long as he got a piece of the pie afterwards. And, with Louis Napoleon’s help, Bismarck was also able to seal a treaty with the Italians, one which stipulated they would get the last of Austria’s holdings in Venetia if they joined a “hypothetical” war against them. By the time 1866 dawned, Franz Josef was isolated on the diplomatic stage — potential allies either ignoring him, or actively hostile.

The one card Austria still had left was its position within the German Confederation. But Bismarck was confident he could get the statelets on his side. That March, the two great rivals began a slow but unstoppable process of mobilization, each new deployment triggering a reaction from the other, until war came to seem inevitable.

By the end of April, Vienna had called a full mobilization. That May, Moltke ordered railway lines to start depositing Prussian troops at the border of Bohemia — part of modern-day Czech Republic, but back then inside the Austrian Empire. On June 1, Austria complained to the German Confederation that Prussia was interfering in its running of Holstein and asked for help.

Since this clearly violated the “no other German states will get involved” clause of the Treaty of Gastein, Bismarck declared Austria had broken the treaty — and that meant war. June 4 dawned with Prussian troops marching into Holstein. Although the Austrian garrison retreated rather than fight in the hopes of averting war, by now everyone was primed for the coming showdown.

Eight days after the Prussians took Holstein, Vienna withdrew its ambassador to Berlin. Two days after that, the German Confederation held a vote. Hanover, Saxony, Bavaria, Württemberg, Baden, Hesse-Darmstadt, and Nassau all agreed to raise forces to help Austria.

Bismarck declared the German Confederation dissolved and prepared to fight them all.

Prussia’s Lightning Strikes Across the German States

At the outset of the Seven Weeks’ War, it would have been tricky to guess who might win. On the one hand, Austria had a population twice the size of Prussia, plus a whole bunch of German statelets onside. On the other, the Prussians were so militarized that their army’s size matched Austria’s.

And they could call on their Italian allies to attack from the south at any time. Yet anyone who focused on relative strengths would have missed the real key development of the last few years. In terms of military technology, Prussia vastly outclassed Austria.

Prussian infantry were armed with new Dreyse “needle” guns that could be reloaded rapidly from a kneeling or lying position. In the background, Moltke had ensured multiple rail lines were ready to transport troops to sensitive points at what was then lightning speed. One of the first fast strikes the Prussians needed to make was knocking out the other German states before they could concentrate their forces.

While on paper Austria had a formidable coalition, in reality that coalition was scattered across Central Europe. Hit the individual armies early, and Prussia would nullify one of Vienna’s big advantages. The result was the war opening with a direct invasion of Bohemia, yes, but also the Prussian 13th Division steaming into Hanover and seizing the capital before Hanover’s forces could even react.

On June 17, the city fell. Although Hanover’s army gamely marched south towards the main action, they were quickly surrounded. On June 29, the Hanoverians surrendered, having fought just a single battle.

The first victims of this chain reaction were the armies of Hesse under Prince Alexander, and the Bavarians under Prince Charles. At the time the Hanoverians surrendered, Hesse and Bavaria were executing a plan to head south and link up — taking a route that separated their two armies with a mountain range. The plan only made sense if the Hanoverians were able to keep the Prussians tied up, but Berlin had dealt with them on the first day of the war.

The result was Prussian troops able to chase down the two armies, then hit the Bavarians in surprise attacks — smashing their forces at Dermbach. While some of Prussia’s forces had been off humiliating Hanover and Bavaria, Moltke’s main focus had been the three vast armies he’d dispatched to Saxony and Bohemia. As the Prussian Army of the Elbe crossed into Saxony, the statelet’s soldiers under Crown Prince Albert had been forced to retreat, escaping into Bohemia.

Saxony had fallen to Prussia by June 16. Moltke’s plan was to use his three armies to drive the Austrians into a corner outside the town of Jičín, where — backs to the River Elbe — they’d be forced to surrender. On June 23, the Prussian First Army entered Bohemia.

Three days later, the Second Army came in over the mountains. Now all that stood between them and ravaging the empire’s lands was Austria’s North Army under Field Marshal Benedek.

The Catastrophe at Königgrätz

Field Marshal Benedek was not confident about taking on Prussia. “Pray conclude peace at any price,” he telegraphed to Franz Josef on July 1, “a catastrophe is inevitable.” Nor was he exaggerating.

From the moment the Prussians first hit the Austrian North Army, the casualty rate had been staggering. In just the four days prior to his gloomy telegram, Benedek had lost some 30,000 men in skirmishes. Bismarck, Moltke, and Wilhelm I — by contrast — were so confident of victory that they left Berlin to come and watch the battle in person.

Trapped near the Elbe outside Königgrätz (today Hradec Králové), Benedek could see the nightmare about to unfold. His own poor deployment of troops along a wide arc would contribute to it. Beginning with a volley from Prussian fusiliers at 06:30am, the Battle of Königgrätz was one of the largest engagements Europe had yet seen — its 450,000 participants making it only a bit smaller than the biggest battles of the Napoleonic Wars.

An hour and a quarter after the battle started, Wilhelm and Bismarck reached Moltke’s command post — a nearly fatal move when a wild shell landed just 18 meters from Wilhelm, nearly blowing him up. But the king survived to see his army triumph. The first few hours were more evenly matched than the outcome might suggest, with the Prussians also taking heavy casualties.

In fact, casualties were so heavy that around noon Wilhelm uneasily asked if there was a plan for retreat. To which Moltke calmly gave his legendary reply: “Here there will be no retreat. We are fighting for the very existence of Prussia.”

By now, though, victory was already assured. Just two hours after Wilhelm got cold feet, Moltke’s men executed a plan to take two hills overlooking the battlefield, from where they began a brutal artillery barrage against the Austrians. A barrage so brutal that the Austrians simply broke ranks and fled.

What followed was a human tide washing toward the Elbe and the handful of pontoon bridges Benedek had set up in case of retreat. So vast were the numbers fleeing that they got trapped in a bottleneck. The Prussians used this as target practice.

Then Benedek — safe on the opposite bank — gave the order to destroy the bridges and everything went from bad to worse, and then from worse to apocalyptic. In panic, scores of soldiers tried to swim to safety across the river, only to drown. The thousands that didn’t were taken prisoner by the Prussians — 20,000 in all, on top of the 24,000 killed and wounded in battle.

The Prussians, by contrast, lost a mere 9,000 men in total. From the opposite bank, Benedek sent a telegram to Franz Josef that simply read: “The catastrophe I warned you of two days ago happened today.”

The Collapse of the German Confederation

News of the debacle at Königgrätz spread across Europe, and the tempo of the war shifted. In the south, the Italians launched their own attack, splitting Vienna’s forces across two fronts. But it was in the German Confederation that the impact was most keenly felt.

Demoralized, the Bavarian army broke off from its original plan of advancing south, high-tailing it instead towards the defensible outpost of Würzburg. This in turn alarmed Prince Alexander of Hesse, who pivoted after them with the federal 8th Corps in tow to stop himself getting picked off. But this created a serious problem.

The 8th Corps had been all that was standing between Prussia and the Confederation’s federal Diet at Frankfurt. Suddenly, the free city was utterly undefended. With what was now clearly Europe’s sleekest war machine bearing down on them, the senators in Frankfurt did the only thing they could.

On July 15, they declared their city open to the invaders. A day later, Prussian troops marched in. One day after that, they annexed the city, along with the neighboring duchy of Nassau.

With Hanover also occupied and other statelets falling fast, it was obvious the war wouldn’t just end with Austria’s humiliation, but also the destruction of the German Confederation itself. The first to accept the inevitable was Austria. With Prussia in control of Bohemia and their forces encroaching on Upper Austria, Franz Josef accepted defeat.

On July 22, the emperor communicated to Wilhelm that he wished to surrender. Remarkably, Wilhelm tried to refuse. With the road to Vienna wide open, he was already entertaining visions of Prussian troops marching through the imperial capital.

But dismantling Austria wasn’t part of the Bismarck plan. When he heard what Wilhelm was hoping to do, Bismarck threatened to hurl himself out a fourth floor window unless the king accepted the surrender. Not wanting to see his best advisor self-defenestrate, Wilhelm grumpily agreed.

With Vienna out of the fight, all that remained was a mopping up operation against Bavaria and the remaining federal forces. Down near Würzburg, the Bavarian Army and the 8th Corps under Prince Alexander had once again come up with a plan that involved separating their armies to march to some distant goal. Once again, the Prussians attacked while they were divided, eventually forcing them to split in different directions, unable to combine their might.

By August 1, the Bavarians were essentially trapped in Würzburg. That same day, the Prussians issued a demand for surrender. Prince Charles raised the white flag, and Prussia’s troops took the city mere hours before the truce came into effect.

The Peace of Prague and the Reshaping of Central Europe

Signed on August 23, the Peace of Prague was a mixture of bad and extremely bad news for Prussia’s opponents. For Austria, the news was merely bad. Franz Josef was forced to surrender Holstein, pay 30 million silver florins indemnity, and permanently abandon any role within German politics.

More painfully, he also had to surrender Venetia to the Italians. Painful, because Austria had actually won the war in the south. But, because Bismarck had promised to keep fighting until the Italians had their prize, Vienna was forced to give it up anyway.

With that, Italian Unification entered its final phase. Only Rome now remained outside Italian control — the last vestige of the Papal States, under the protection of Napoleon III. Just four years later, the Franco-Prussian War would remove that protection, and Italy would be complete.

Bad as the peace was for Austria, for the German states it was catastrophic. Rather than negotiate, Bismarck simply annexed Hanover, Hesse-Kassel, Nassau, and Frankfurt into Prussia. He then created something called the North German Confederation, and forced all states above the River Main to join it.

Only Baden, Hesse-Darmstadt, Württemberg, and Bavaria remained independent. Yet, while it was called a “confederation,” the North German Confederation was simply a vessel for Prussian dominance. A vessel that, five years later, would merge with those remaining independent states into a behemoth called Germany.

The last major change came the following year, in 1867. With his authority so weakened following the disastrous war, Franz Josef was forced to forge a compromise with his empire’s Hungarian minority to stop them declaring independence. From then on, there would be no mere “Austria” straddling Central Europe, but a Dual Monarchy known to history as the Austro-Hungarian Empire.

The Seven Weeks’ War lies at the more obscure end of European conflicts, often overshadowed by the larger Franco-Prussian War, if it is remembered at all. Yet, despite its lack of renown, it remains one of the defining moments in history. Although they would be completed later, the rise of Germany and Italy can both be traced to this one short war.

Everything that came next — the German Empire, the war with France, World War I — all found their seeds in 1866. Semi-forgotten now, the effects of this one short conflict continue to shape Europe to this day.

Frequently Asked Questions

What caused the Seven Weeks’ War between Prussia and Austria?

The immediate trigger was the dispute over the administration of Schleswig and Holstein, two duchies Prussia and Austria had jointly taken from Denmark in 1864. Under the Treaty of Gastein, Holstein went to Austria and Schleswig to Prussia. Bismarck used Austria’s complaint to the German Confederation about Prussian interference in Holstein as the legal pretext to declare Austria had broken the treaty, launching the war on June 4, 1866. The deeper cause was Bismarck’s long-running ambition to drive Austria out of German affairs and unite the German states under Prussian leadership.

Why did Prussia win the Battle of Königgrätz so decisively?

Prussia’s Dreyse needle guns allowed infantry to reload rapidly from a kneeling or prone position, giving them a devastating rate of fire against Austrian troops standing to reload. Chief of Staff Helmuth von Moltke had also built a rail-based logistics system that could move large armies to critical points at extraordinary speed. At Königgrätz itself on July 3, 1866, Moltke coordinated three separate armies to converge on Field Marshal Benedek’s North Army. When Prussian artillery seized two overlooking hills and opened a barrage, the Austrians broke and fled, losing 44,000 men against Prussia’s 9,000.

How did Bismarck isolate Austria diplomatically before the war?

Bismarck made quiet diplomatic rounds while he and Vienna were still haggling over the Schleswig-Holstein settlement. Russia was still angry at Austria for perceived betrayal during the Crimean War. Britain had been alienated by the joint Prussian-Austrian attack on Denmark. Napoleon III of France was willing to stand aside in exchange for territorial compensation afterward.

Most crucially, Bismarck sealed a treaty with Italy, promising them Austria’s remaining province of Venetia if they joined a war against Vienna. By 1866, Austria stood almost friendless.

What were the terms of the Peace of Prague?

Signed on August 23, 1866, the Peace of Prague required Austria to surrender Holstein, pay a thirty million silver florin indemnity, permanently withdraw from German politics, and hand Venetia to Italy—despite Austria having won the war on its southern front. For the German states that had sided with Austria, terms were harsher: Bismarck simply annexed Hanover, Hesse-Kassel, Nassau, and Frankfurt into Prussia and forced all states north of the River Main into the new North German Confederation under Prussian leadership.

What were the long-term consequences of the Seven Weeks’ War?

The war ended the German Confederation and replaced it with Prussian-dominated structures that five years later merged into the German Empire. Austria, humiliated and weakened, was forced in 1867 to share power with Hungary, creating the Austro-Hungarian Dual Monarchy. Italy gained Venetia, advancing its own unification to the point where only Rome remained outside Italian control. And the North German Confederation provided Bismarck the vehicle he needed to unite the remaining German states when war with France arrived in 1870.

Sources

1. http://www.historyofwar.org/articles/wars_austro_prussian.html
2. https://warfarehistorynetwork.com/2016/09/28/the-art-of-victory-koniggratz-1866/
3. https://play.acast.com/s/whendiplomacyfails/wdfrem-1-thefranco-prussianwari
4. https://www.britannica.com/event/Battle-of-Koniggratz
5. https://youtu.be/LFtz5ZTJxxw