Eventually the Olivier tendency prevailed, and through a series of reforms implemented between 1867 and 1870 the constitution of the empire was changed in a distinctly liberal-parliamentary sense. The transformation carried out was sanctioned on 8 May 1870 by an imposing popular plebiscite: seven and a half million votes in favor against one and a half million opponents.
According to Programingplease, the consensus of the huge majority of the population thus seemed to support the liberal empire that succeeded the authoritarian empire. But the building was now undermined at its foundations. The adversaries did not disarm, and could profit from their bitter campaign of sensational scandals, such as that caused by the killing of the journalist Victor Noir by the prince of the imperial family, Pietro Bonaparte (January 1870). A strong shock would have been enough to bring about the collapse. It came, as it was fatal, from foreign policy, in connection with the clearly anti-Prussian policy that Napoleon III carried out after the failure of the attempts of 1867, and of which the first manifestation was the attempt made between 1868 and 1869 to establish with the ‘Austria and Italy a triple aimed at isolating and crushing the state of the Hohenzollerns. The attempt, after arriving at the preparation of a draft treaty (May 1869), ran aground due to the Napoleonic refusal to accept the condition set by the Italian government of the French mackerel from Rome, but left the atmosphere of Frankish relations increasingly clouded. – Prussians. The Prussian desire, embodied in Bismarck and Moltke, to complete the Germanic unity against France, responded beyond the Rhine to French suspicions and aversions against Prussia. As a French publicist, L.-A. Prévost-Paradol, France and Prussia were like two locomotives rushing at great speed on the same track. The collision was fatal.
The superior ability of Bismarck was to provoke him and to make him happen on the question of the candidacy of a prince Hohenzollern to the vacant throne of Spain, a question in which the second empire took the position of the aggressor, very apt to arouse around Prussia the sympathy and solidarity of all Germans. The controversy, which was poisoned at the beginning of the summer of 1870, fell into shock when the dispatch skillfully manipulated by Bismarck spread, which disclosed the news of the refusal opposed by the King of Prussia to accept the French demands presented by Ambassador Benedetti in the Ems interview. Plunging into the French excited environment, the communiqué seemed a challenge and determined the irresistible increase and the triumph of the warlike currents, which Thiers tried in vain to resist. The declaration of war was decided and sent to Berlin: the Empire entrusted its fate to the fortune of arms, facing the struggle against the powers of the old anti-Napoleonic coalition of 1813-1814 for the third time. After the struggles against Russia and Austria, it was the turn of the struggle against Prussia. A little more than a month was enough to demonstrate the immensity of the error. Diplomatically isolated, because the efforts to resume the ranks of the alliance project of 1869, poorly prepared militarily, were unsuccessful, the second empire found itself faced with a Prussia that Bismarck had been able to support on all the Germanic forces immediately gathered against the centuries-old adversary., and on the benevolent neutrality of England and Russia, while Moltke had fashioned her a formidable instrument of war. After the French attempts to advance beyond the Rhine, immediately cut short, followed the lightning and terrible invasion of the German forces in Alsace and Lorraine. And on September 2, one of the two armies into which the imperial forces were divided capitulated at Sedan with the same emperor, while the other was tightly locked in Metz.
The inevitable immediate backlash of these disasters was the collapse of the empire. On 4 September in Paris the republican elements succeeded without resistance in proclaiming the decline of the dynasty and the advent of the republic, with a provisional government of national defense at the head. The now numerous offshoots that the republican party had, especially in the southern and eastern regions, allowed a prompt expansion of the Paris movement throughout the country. The second empire was over. For the precedents of the dynasty that governed it and for the ways and the program with which it arose, it had as its irreplaceable basis the successes and victories, the enlargements: the defeats and the invasion suddenly deprived it of all consistency.