<P> At the Congress of Vienna in 1815, Metternich and his conservative allies had reestablished the Spanish monarchy under King Ferdinand VII . Over the following forty years, the great powers supported the Spanish monarchy, but events in 1868 would further test the old system . A revolution in Spain overthrew Queen Isabella II, and the throne remained empty while Isabella lived in sumptuous exile in Paris . The Spanish, looking for a suitable Catholic successor, had offered the post to three European princes, each of whom was rejected by Napoleon III, who served as regional power - broker . Finally, in 1870 the Regency offered the crown to Leopold of Hohenzollern - Sigmaringen, a prince of the Catholic cadet Hohenzollern line . The ensuing furor has been dubbed by historians as the Hohenzollern candidature . </P> <P> Over the next few weeks, the Spanish offer turned into the talk of Europe . Bismarck encouraged Leopold to accept the offer . A successful installment of a Hohenzollern - Sigmaringen king in Spain would mean that two countries on either side of France would both have German kings of Hohenzollern descent . This may have been a pleasing prospect for Bismarck, but it was unacceptable to either Napoleon III or to Agenor, duc de Gramont, his minister of foreign affairs . Gramont wrote a sharply formulated ultimatum to Wilhelm, as head of the Hohenzollern family, stating that if any Hohenzollern prince should accept the crown of Spain, the French government would respond--although he left ambiguous the nature of such response . The prince withdrew as a candidate, thus defusing the crisis, but the French ambassador to Berlin would not let the issue lie . He approached the Prussian king directly while Wilhelm was vacationing in Ems Spa, demanding that the King release a statement saying he would never support the installation of a Hohenzollern on the throne of Spain . Wilhelm refused to give such an encompassing statement, and he sent Bismarck a dispatch by telegram describing the French demands . Bismarck used the king's telegram, called the Ems Dispatch, as a template for a short statement to the press . With its wording shortened and sharpened by Bismarck--and further alterations made in the course of its translation by the French agency Havas--the Ems Dispatch raised an angry furor in France . The French public, still aggravated over the defeat at Sadová, demanded war . </P> <P> Napoleon III had tried to secure territorial concessions from both sides before and after the Austro - Prussian War, but despite his role as mediator during the peace negotiations, he ended up with nothing . He then hoped that Austria would join in a war of revenge and that its former allies--particularly the southern German states of Baden, Württemberg, and Bavaria--would join in the cause . This hope would prove futile since the 1866 treaty came into effect and united all German states militarily--if not happily--to fight against France . Instead of a war of revenge against Prussia, supported by various German allies, France engaged in a war against all of the German states without any allies of its own . The reorganization of the military by von Roon and the operational strategy of Moltke combined against France to great effect . The speed of Prussian mobilization astonished the French, and the Prussian ability to concentrate power at specific points--reminiscent of Napoleon I's strategies seventy years earlier--overwhelmed French mobilization . Utilizing their efficiently laid rail grid, Prussian troops were delivered to battle areas rested and prepared to fight, whereas French troops had to march for considerable distances to reach combat zones . After a number of battles, notably Spicheren, Wörth, Mars la Tour, and Gravelotte, the Prussians defeated the main French armies and advanced on the primary city of Metz and the French capital of Paris . They captured Napoleon III and took an entire army as prisoners at Sedan on 1 September 1870 . </P> <P> The humiliating capture of the French emperor and the loss of the French army itself, which marched into captivity at a makeshift camp in the Saarland ("Camp Misery"), threw the French government into turmoil; Napoleon's energetic opponents overthrew his government and proclaimed the Third Republic . The German High Command expected an overture of peace from the French, but the new republic refused to surrender . The Prussian army invested Paris and held it under siege until mid-January, with the city being "ineffectually bombarded". On 18 January 1871, the German princes and senior military commanders proclaimed Wilhelm "German Emperor" in the Hall of Mirrors at the Palace of Versailles . Under the subsequent Treaty of Frankfurt, France relinquished most of its traditionally German regions (Alsace and the German - speaking part of Lorraine); paid an indemnity, calculated (on the basis of population) as the precise equivalent of the indemnity that Napoleon Bonaparte imposed on Prussia in 1807; and accepted German administration of Paris and most of northern France, with "German troops to be withdrawn stage by stage with each installment of the indemnity payment". </P>

What was significant about the unifications of italy and germany