linguistic:paraphrasing, quality:correction, information:highlighting, structural:summarization
A last search for allies

Napoleon III was overconfident in his military strength and went into war even after he failed to find any allies who would support a war to stop German unification.

Following the defeat of Austria, Napoleon resumed his search for allies against Prussia. In April 1867, he proposed an alliance, defensive and offensive, with Austria. If Austria joined France in a victorious war against Prussia, Napoleon promised that Austria could form a new confederation with the southern states of Germany and could annex Silesia, while France took for its part the left bank of the Rhine River. But the timing of Napoleon's offer was poorly chosen; Austria was in the process of a major internal reform, creating the new Dual Monarchy of Austria-Hungary.

Napoleon's attempt to install the Archduke Maximilian, the brother of the Austrian Emperor, in Mexico was just coming to its disastrous conclusion; the French troops had just been withdrawn from Mexico in February 1867, and the unfortunate Maximilian would be captured, judged and shot by a firing squad on 19 June. Napoleon III made these offers again in August 1867, on a visit to offer condolences for the death of Maximilian, but the proposal was not received with enthusiasm.

Napoleon III also made one last attempt to persuade Italy to be his ally against Prussia. Italian King Victor Emmanuel was personally favorable to a better relationship with France, remembering the role that Napoleon III had played in achieving Italian unification, but Italian public opinion was largely hostile to France; on 3 November 1867, French and Papal soldiers had fired upon the Italian patriots of Garibaldi, when he tried to capture Rome. Napoleon presented a proposed treaty of alliance on 4 June 1869, the anniversary of the joint French-Italian victory at Magenta. The Italians responded by demanding that France withdraw its troops who were protecting the Pope in Rome. Given the opinion of fervent French Catholics, this was a condition Napoleon III could not accept.

While Napoleon III was having no success finding allies, Bismarck signed secret military treaties with the southern German states, who promised to provide troops in the event of a war between Prussia and France. In 1868, Bismarck signed an accord with Russia that gave Russia liberty of action in the Balkans in exchange for neutrality in the event of a war between France and Prussia. This treaty put additional pressure on Austria-Hungary, which also had interests in the Balkans, not to ally itself with France.

But most importantly, Prussia promised to support Russia in lifting the restrictions of the Congress of Paris. "Bismarck had bought Tsar Alexander II's complicity by promising to help restore his naval access to the Black Sea and Mediterranean (cut off by the treaties ending the Crimean War), other powers were less biddable". Bismarck also reached out to the liberal government of William Gladstone in London, offering to protect the neutrality of Belgium against a French threat. The British Foreign Office under Lord Clarendon mobilized the British fleet, to dissuade France against any aggressive moves against Belgium. In any war between France and Prussia, France would be entirely alone.

In 1867, French politician Adolphe Thiers (who became President of the French Republic in 1871) accused Napoleon III of erroneous foreign policy: "There is no mistake that can be made". Bismarck thought that French vanity would lead to war; he exploited that vanity in the Ems Dispatch in July 1870. France took the bait and declared war on Prussia, which proved to be a major miscalculation. This allowed Bismarck and Prussia to present the war to the world as defensive, although Prussia and Bismarck had aggressive plans, and they soon became known in relation to the annexation of the French provinces of Alsace-Lorraine.