Causes of the Franco - Prussian War The causes of the Franco - Prussian War are deeply rooted in the events surrounding the German unification . In the aftermath of the Austro - Prussian War ( 1866 ) , Prussia had annexed numerous territories and formed the North German Confederation . This new power destabilized the European balance of power established by the Congress of Vienna ( 1815 ) after the Napoleonic Wars . Prussia then turned its attention towards the south of Germany , where it sought to expand its influence . France was strongly opposed to the annexation of the Southern German States ( Bavaria , Wurttemberg , Baden and Hesse ) , which would have created a too powerful country next to its border . In Prussia , a war against France was deemed necessary to arouse German nationalism in those States that would allow the unification of a great German empire . This aim was epitomized by Prussian Chancellor Otto von Bismarck ' s quote : " I knew that a Franco - Prussian War must take place before a united Germany was formed . " Bismarck also knew that France should be regarded as the aggressor in the conflict to bring the Southern German States to side with Prussia , hence giving Germans numerical superiority . However , the immediate cause of the war resides in the candidacy of a Prussian prince to the throne of Spain , France feared encirclement by an alliance between Prussia and Spain . The Hohenzollern prince ' s candidacy was withdrawn under French diplomatic pressure , but Otto von Bismarck goaded the French into declaring war by altering a telegram sent by William I . Releasing the Ems Telegram to the public , Bismarck made it sound as if the king had treated the French envoy in a demeaning fashion . Six days later , France declared war on Prussia and Southern German States immediately sided with Prussia . French Emperor Napoleon III and Prime Minister Émile Ollivier ' s eagerness to relieve France from internal political convulsions also contributed to France ' s declaration of war on Prussia . European wars and the balance of power : 1865 – 1866 . In October 1865 , Napoleon III , ruler of France , met with Prussian Prime Minister Otto von Bismarck in Biarritz , France . It was there that the two men struck a deal — France would not get involved in any future actions between Prussia and Austria or ally herself with Austria if Prussia did not allow Austria to claim Venetia . When Austria and Prussia met in May 1866 , Bismarck honored the agreement made in Biarritz the previous year and refused to allow Austria to have Venetia . Austria then attempted to guarantee Italy Venetia if they remained neutral , but the two nations were unable to agree on a suitable arrangement as an alliance formed earlier in the year bound Italy to Prussia . Napoleon III then committed a serious blunder by agreeing with Austria in a treaty to accept Venetia by allowing Austria to go to war with Prussia , a move which violated the agreement Napoleon had made with Bismarck . After Prussia emerged victorious over the Austrian army at the Battle of Königgrätz ( also known as Sadowa or Sadová ) in the Austro - Prussian War of 1866 , negotiations were being held between Austria and Prussia in July and August of that year . It was during that period that Napoleon III first discovered that a bladder stone was causing him great pains , created from gonorrhea l infection . His condition was so bad during those negotiations that he was forced to retire to Vichy to recuperate , removing himself from Paris . Although the emperor favored neutrality as to not upset events , certain members of his circle thought it was an unwise move , considering the opportunity to prevent Prussia from becoming too strong . One of these men , foreign minister Édouard Drouyn de Lhuys , convinced the emperor to plant 80 , 000 men on the eastern border to convince Wilhelm I to maintain the balance of power in Europe . Despite this important victory , de Lhuys was subverted by several other ministers , and Napoleon III changed his mind , reverting to a position of neutrality . This change of heart would end up causing de Lhuys to ultimately lose his position . Napoleon III ' s wife Empress Eugénie , who took an active part throughout his rule , referred to this time much later as " the critical date , the Empire ' s fatal date ; it was during these months of July and August that our fate was sealed ! Of all that period , there is not a single fact , not a single detail that has not remained in my mind . " Franz Joseph of Austria accepted Bismarck ' s terms under the Peace of Prague . Using this to his advantage , Bismarck declared the German Confederation of 1815 null and void , and created a new network of states under Prussian control . Frankfurt - am - Main , Hannover , Hesse - Kassel ( or Hesse - Cassel ) , Holstein , Nassau , and Schleswig were annexed outright while Hesse - Darmstadt , Mecklenburg , Saxony , the Thuringian duchies , as well as the cities of Bremen , Hamburg , and Lübeck were combined into a new North German Confederation that governed nominally and was actually controlled by Prussia herself . Bismarck was approached soon after the end of the war by Napoleon III ' s ambassador to Prussia , Vincent Benedetti . Benedetti brought with him a secret proposal by Napoleon III that France would approve of Bismarck ' s acquisition of the northern German states and their control over the southern German states if Prussia remained neutral while France annexed Belgium and Luxembourg . France had earlier guaranteed the independence of Belgium in the Treaty of London in 1839 as an " " independent and perpetually neutral state " " , making the proposal a tacit agreement to break their promise . Bismarck was very surprised since he had already gained a powerful position in Europe by the armistice , and called Napoleon III ' s request among others later " " like ' an innkeeper ' s bill ' or a waiter asking for ' a tip ' . " " He asked Benedetti to provide the proposal in writing , and the ambassador obliged his request . This document was to be important to Bismarck later on , to great effect . The true views of Napoleon III on the subject of the balance of power in Europe can be found in a state circular handed to every diplomatic representative for France . In this paper dated September 1 , 1866 , the emperor saw the future of Europe after the Peace of Prague in this manner : Domestic agenda in France and Prussia . French prestige and politics . France ' s position in Europe was now in danger of being overshadowed by the emergence of a powerful Prussia , and France looked increasingly flat - footed following Bismarck ' s successes . In addition , French ruler Napoleon III was on increasingly shaky ground in domestic politics . Having successfully overthrown the Second Republic and established the Bonapartist Second Empire , Napoleon III was confronted with ever more virulent demands for democratic reform from leading republicans such as Jules Favre , along with constant rumours of impending revolution . In addition , French aspirations in Mexico had suffered a final defeat with the execution of the Austrian - born , French puppet Emperor Maximilian I of Mexico in 1867 . The French imperial government now looked to a diplomatic success to stifle demands for a return to either a republic or a Bourbon monarchy . A war with Prussia and resulting territorial gains in the Rhineland and later Luxembourg and Belgium seemed the best hope to unite the French nation behind the Bonapartist dynasty . With the resulting prestige from a successful war , Napoleon III could then safely suppress any lingering republican or revolutionary sentiment behind reactionary nationalism and return France to the center of European politics . Bismarck and German nationalism . Prussia in turn was also beset with problems . While revolutionary fervour was far more muted than in France , Prussia had in 1866 acquired millions of new citizens as a result of the Austro - Prussian War , which was also a civil war among German states . The remaining German kingdoms and principalities maintained a steadfastly parochial attitude towards Prussia and German unification . The German princes insisted upon their independence and balked at any attempt to create a federal state that would be dominated by Berlin . Their suspicions were heightened by Prussia ' s quick victory and subsequent annexations . Before the war , only some Germans , inspired by the recent unification of Italy , accepted and supported what the princes began to realise , that Germany must unite in order to preserve the fruit of an eventual victory . Bismarck had an entirely different view after the war in 1866 , he was interested only in strengthening Prussia through the eyes of a staunch realist . Uniting Germany appeared immaterial to him unless it improved Prussia ' s position . Bismarck had mentioned before the war the possibility of ceding territory along the Rhine to France , and Napoleon III , urged by his representatives in France , used these casual references by Bismarck to press for more of the territory that Prussia had received from Austria . These discussions , leaked by Bismarck to the German states in the south , turned former enemies into allies almost overnight , receiving not only written guarantees but armies that would be under the control of Prussia . Alliances and diplomacy . German states . Diplomatically and militarily , Napoleon III looked for support from Austria , Denmark , Bavaria , Baden , and Württemberg , as all had recently lost wars against Prussia . However , Napoleon III failed to secure revanchist alliances from these states . Denmark had twice fought Prussia during the First and Second Wars of Schleswig ( a stalemate in the 1848 – 50 , and a defeat in 1864 against a confederation of North German states and Austria under the leadership of Prussia ) , and was unwilling to confront Prussia again . As part of the settlement of the Austro - Prussian War in 1866 , secret treaties of mutual defense were signed between Prussia and Bavaria , Baden , and Württemberg . What made them especially significant was that not only were they secret , giving Napoleon III a false sense of security , but Bismarck had used Napoleon III ' s earlier demand of territory along the Rhine to drive the southern German states into his arms . By these treaties , Prussia would defend all of the southern German states with its military power as long as their states joined the Northern Confederation in defense of Prussia . It was a bargain that would gravely threaten the French " empereur " and his designs on restoring French pride . Austria and Italy . The Austrian Chancellor Count Friedrich Ferdinand von Beust was " impatient to take his revenge on Bismarck for Sadowa . " As a preliminary step , the " Ausgleich " with Hungary was " rapidly concluded . " Beust " persuaded Francis Joseph to accept Magyar demands which he had till then rejected . " . However , Austria would not support France unless Italy was part of the alliance . Victor Emmanuel II and the Italian government wanted to support France , but Italian public opinion was bitterly opposed so long as Napoleon III kept a French garrison in Rome protecting Pope Pius IX , thereby denying Italy the possession of its capital ( Rome had been declared capital of Italy in March 1861 , when the first Italian Parliament had met in Turin ) . Napoleon III made various proposals for resolving the Roman Question , but Pius IX rejected them all . Despite his previous support for Italian unification , Napoleon did not wish to press the issue for fear of angering Catholics in France . Raffaele De Cesare , an Italian journalist , political scientist , and author , noted that : Another reason why Beusts ' s desired " revanche " against Prussia did not materialize was the fact that , in 1870 , the Hungarian Prime Minister Gyula Andrássy was " vigorously opposed . " Russia . In addition to the problems facing Napoleon III in obtaining potential allies , Bismarck worked feverishly to isolate France from the other European powers . Since 1863 , Bismarck had made efforts to cultivate Russia , co - operating , amongst other things , in dealing with Polish insurgents . This important move gained for Bismarck the neutrality of Russia if Prussia went to war , and it also prevented Austria from taking sides with France as Austria fully supported the Poles . When Alexander II came to France on an official visit in 1867 , he was at the receiving end of an unsuccessful assassination attempt by Polish - born Anton Berezovski while riding with Napoleon III and the Empress Eugenie . Tsar Alexander was very offended that not only had the French courts given Berezovski imprisonment instead of death , but the French press had sided with the Pole rather than Alexander . This experience forever shattered his views of France , and saw in the reaction his visit had received why his father had despised the French . In 1868 he held discussions with the Prussians , intending to counter a possible Austrian alliance with Napoleon III by Franz Joseph . If German forces were , for any reason , bogged down in the west , then Prussia ' s eastern and southern flanks would have been highly vulnerable . With his usual skill , Bismarck moved carefully to sidestep the nightmare . The Russian government even went so far as to promise to send an army of 100 , 000 men against the Austrians if Austria joined France in a war against Prussia . Whilst at Ems in the crucial summer of 1870 Wilhelm I and Bismarck had meetings with Tsar Alexander , also present in the spa town . Alexander , though not naturally pro - German , became very comfortable with Prussian suggestions . Bismarck also had talks at Ems with Alexander Mikhailovich Gorchakov , the Russian Foreign Minister , and was assured in mid July , days before the French declaration of war , that the agreement of 1868 still held : in the event of Austrian mobilisation , the Russians confirmed that they would send 300 , 000 troops into Galicia . Bismarck now had all he wanted : a counter to Austria and the assurance of a one - front war . United Kingdom . Bismarck then made Benedetti ' s earlier draft public to " The Times " in London that demanded Belgium and Luxembourg as the price for remaining neutral during the Austro - Prussian War . Sensitive to the threat of a major power controlling the strategically significant Low Countries and the English Channel coastline , the United Kingdom government in particular took a decidedly cool attitude to these French demands , and the British people were disturbed by this subversive attempt at going back on Napoleon III ' s word . Therefore , Britain as a nation did nothing to aid France . The Prime Minister , William Gladstone , expressed his thoughts on the matter to Queen Victoria by writing to her that " " Your majesty will , in common with the world , have been shocked and startled . " " Though it had enjoyed some time as the leading power of continental Europe , the French Empire found itself dangerously isolated . Monarchial crises . Luxembourg crisis . The king of the Netherlands , William III , was under a personal union with Luxembourg that guaranteed its sovereignty . Napoleon III had taken note that the king had amassed certain personal debts that would make a sale of Luxembourg to France possible . However , Luxembourg lies astride one of the principal invasion routes an army would use to invade either France or Germany from the other . The city of Luxembourg ' s fortifications were considered " the Gibraltar of the North " , and neither side could tolerate the other controlling such a strategic location . The pressure on Bismarck to object not only came from his monarch William I , but from Chief of Staff of the Prussian army Helmuth von Moltke . Moltke had additional reason to object - he desired war with France , stating flatly that " " Nothing could be more welcome to us than to have now the war that we must have . " " Bismarck balked at such talk about war . He refused to actually engage France on the basis that he firmly believed that Prussia would gain a far more decisive advantage by merely opposing the sale , and that Napoleon III could be thwarted due to his fear of war with Prussia . Assuming that Bismarck would not object , the French government was shocked to learn that instead Bismarck , Prussia and the North German Confederation were threatening war should the sale be completed . Napoleon III had let precious months peel away in trying to complete the transaction , allowing Bismarck time to rally support to Prussia ' s objection . To mediate the dispute , the United Kingdom hosted the London Conference ( 1867 ) attended by all European great powers . It confirmed Luxembourg ' s independence from the Netherlands and guaranteed its independence from all other powers . War appeared to have been averted , at the cost of thwarting French desires . The Spanish throne had been vacant since the revolution of September 1868 , and the Spanish offered the throne to the German prince Leopold of Hohenzollern - Sigmaringen , a Catholic as well as a distant cousin of King Wilhelm of Prussia . Leopold and Wilhelm I were both uninterested , but the wily Bismarck was acutely interested as it was an opportunity to once again best Napoleon III . Bismarck persuaded Leopold ' s father to accept the offer for his nation , and it was accepted instead by Leopold himself in June 1870 . The Hohenzollern crisis and the Ems Dispatch . On 2 July 1870 , " " Marshall Prim [ who held power in Spain ] announced in Madrid that the Spanish government had offered the crown of Spain to Prince Leopold of Hohenzollern . " " Fearing that a Hohenzollern king in Prussia and another one in Spain would put France into a two - front situation , France this time was determined to stand up to the expansion of Prussian influence . Napoleon III at this time was suffering the most unbearable pain from his stones , and the Empress Eugénie essentially was charged with countering the designs of Prussia . She had a vital interest in the crisis as she was of Spanish blood and a member of the royal line . The secretary of foreign affairs , Duc Antoine de Gramont , was directed by the Empress to be the principal instrument by which France would press for war should Leopold ascend the throne . Gramont delivered a speech in front of the " Chambre législative " , proclaiming that " " We shall know how to fulfill our duty without hesitation and without weakness . " " The fatal mistake would soon come as a result of Gramont ' s inexperience , for he counted on alliances that only existed in his mind . " The French press immediately protested the prospect of a Hohenzollern on the Spanish throne , and on 6 July the new Foreign Minister , the Duc de Gramont [ . . . ] told the Chamber that France would not permit Prince Leopold to become King of Spain . [ The French Premier Emile ] Ollivier added that he had no doubt that Prussia would yield in the face of French firmness , but that ' if war be necessary , the government will not enter upon it without the consent of the Legislative Body . ' Gramont ' s statement and Ollivier ' s mention of war were greeted with great enthusiasm by the deputies , and in the public galleries the ladies rose to their feet and waved their handkerchiefs as they joined in the wild applause . Next day the Paris press called for war with Prussia , and on 8 July their language was even more violent . The government instructed [ Comte Vincente ] Benedetti , the French ambassador to Prussia , to demand that King William should publicly refuse his consent to Prince Leopold ' s acceptance of the throne of Spain . " " On 11 July , Benedetti spoke to King William at the watering spa at Ems , and asked him to refuse his consent to Prince Leopold ' s candidature ; Bismarck was on holiday at his estates in East Prussia . King William agreed to order Prince Leopold to withdraw . Ollivier announced the Prussian surrender in the Chamber on 12 July and hailed it as a French triumph and a Prussian humiliation . Bismarck thought the same and considered resigning as Prime Minister . Gramont and Ollivier did not conceal their regret that the Prussians had given in ; and the deputies and most of the press were disappointed that that there was to be no war . [ . . . ] Louis Napoleon sensed the public regret that there would be no war . ' The country will be disappointed , ' he cabled to Ollivier on 12 July ; ' but what can we do ? ' He was in complete agreement with the decision which was taken by the Cabinet on the same day to ask for further guarantees from Prussia and to require King William to give an undertaking that he would never in the future allow Prince Leopold to accept the crown of Spain . When Benedetti confronted King William on the promenade at Ems on the afternoon of 13 July and asked him to give this undertaking , the King was annoyed , refused to do so , and walked away a little abruptly . " Following this direct confrontation , which had bypassed diplomatic protocols , King Wilhelm then sent a message to Berlin reporting this event with the French ambassador , and Bismarck shrewdly edited it to make it " " like a red tag to the bull " " for the French government . The dispatch was edited as follows ( with the words sent in bold ) : Count Benedetti spoke to me on the promenade , in order to demand from me , finally in a very importunate manner , that I should authorize him to telegraph at once that I bound myself for all future time never again to give my consent if the Hohenzollerns should renew their candidature . " I refused at last somewhat sternly , as it is neither right nor possible to undertake engagements of this kind à tout jamais . Naturally I told him that I had as yet received no news , and as he was earlier informed about Paris and Madrid than myself , he could clearly see that my government once more had no hand in the matter . His Majesty has since received a letter from the Prince . " His Majesty " having told Count Benedetti that he was awaiting news from the Prince " , has decided " with reference to the above demand , upon the representation of Count Eulenburg and myself " , not to receive Count Benedetti again , but only to let him be informed through an aide - de - camp that his Majesty " had now received from the Prince confirmation of the news which Benedetti had already received from Paris , and " had nothing further to say to the ambassador . " His Majesty leaves it to your Excellency whether Benedetti ' s fresh demand and its rejection should not be at once communicated both to our ambassadors and to the press . " This dispatch made the encounter more heated than it really was . Known as the Ems Dispatch , it was released to the press . It was designed to give the French the impression that King Wilhelm I had insulted the French Count Benedetti , and to give the Prussian people the impression that the Count had insulted the King . It succeeded in both of its aims - Gramont called it " " a blow in the face of France " " , and the members of the French legislative body spoke of taking " " immediate steps to safeguard the interests , the security , and the honor of France . " " On 19 July 1870 " " Le Sourd , the French Chargé d ' Affaires , delivered Napoleon ' s declaration of war at the Foreign Office " " in Berlin . According to the secret treaties signed with Prussia and in response to popular opinion , Bavaria , Baden , and Württemberg mobilised their armies and joined the war against France . European Public Reaction . At the outbreak of the war , European public opinion heavily favored the Germans . For example , many Italians attempted to sign up as volunteers at the Prussian embassy in Florence , and a Prussian diplomat visited Giuseppe Garibaldi in Caprera . After the fall of Napoleon III following the Battle of Sedan , Bismarck ' s demand for the return of Alsace caused a dramatic shift in that sentiment , which was best exemplified by the reaction of Garibaldi soon after the revolution in Paris , who told the " Movimento " of Genoa on 7 September 1870 that " " Yesterday I said to you : war to the death to Bonaparte . Today I say to you : rescue the French Republic by every means . " "