Negotiations were resumed with Napoleon for the evacuation of Rome by the French troops; but the emperor, though he saw that the temporal power could not for ever be supported by French bayonets, desired some guarantee that the evacuation should not be followed, at all events immediately, by an Italian occupation, lest Catholic opinion should lay the blame for this upon France. Ultimately the two governments concluded a convention on the 15th of September 1864, whereby France agreed to withdraw her troops from Rome so soon as the papal army should be reorganized, or at the outside within two years, Italy undertaking not to attack it nor permit others to do so, and to transfer the capital from Turin to some other city within six months.[18] The change of capital would have the appearance of a definite abandonment of the _Roma capitale_ programme, although in reality it was to be merely a _tappa_ (stage) on the way. The convention was kept secret, but the last clause leaked out and caused the bitterest feeling among the people of Turin, who would have been resigned to losing the capital provided it were transferred to Rome, but resented the fact that it was to be established in any other city, and that the convention was made without consulting parliament. Demonstrations were held which were repressed with unnecessary violence, and although the change of capital was not unpopular in the rest of Italy, where the _Piemontesismo_ of the new régime was beginning to arouse jealousy, the secrecy with which the affair was arranged and the shooting down of the people in Turin raised such a storm of disapproval that the king for the first time used his privilege of dismissing the ministry. Under La Marmora's administration the September convention was ratified, and the capital was transferred to Florence the following year. This affair resulted in an important political change, for the Piedmontese deputies, hitherto the bulwarks of moderate conservatism, now shifted to the Left or constitutional opposition.
Meanwhile, the Venetian question was becoming more and more acute. Every Italian felt the presence of the Austrians in the lagoons as a national humiliation, and between 1859 and 1866 countless plots were hatched for their expulsion. But, in spite of the sympathy of the king, the attempt to raise armed bands in Venetia had no success, and it became clear that the foreigner could only be driven from the peninsula by regular war. To wage this alone Italy was still too weak, and it was necessary to look round for an ally. Napoleon was sympathetic; he desired to see the Austrians expelled, and the Syllabus of Pius IX., which had stirred up the more aggressive elements among the French clergy against his government, had brought him once more into harmony with the views of Victor Emmanuel; but he dared not brave French public opinion by another war with Austria, nor did Italy desire an alliance which would only have been bought at the price of further cessions. There remained Prussia, which, now that the Danish campaign of 1864 was over, was completing her preparations for the final struggle with Austria for the hegemony of Germany; and Napoleon, who saw in the furthering of Bismarck's plans the surest means of securing his own influence in a divided Europe, willingly lent his aid in negotiating a Prusso-Italian alliance. In the summer of 1865 Bismarck made formal proposals to La Marmora; but the _pourparlers_ were interrupted by the conclusion of the convention of Gastein (August 14), to which Austria agreed partly under pressure of the Prusso-Italian _entente_. To Italy the convention seemed like a betrayal; to Napoleon it was a set-back which he tried to retrieve by suggesting to Austria the peaceful cession of Venetia to the Italian kingdom, in order to prevent any danger of its alliance with Prussia. This proposal broke on the refusal of the emperor Francis Joseph to cede Austrian territory except as the result of a struggle; and Napoleon, won over by Bismarck at the famous interview at Biarritz, once more took up the idea of a Prusso-Italian offensive and defensive alliance. This was actually concluded on the 8th of April 1866. Its terms, dictated by a natural suspicion on the part of the Italian government, stipulated that it should only become effective in the event of Prussia declaring war on Austria within three months. Peace was not to be concluded until Italy should have received Venetia, and Prussia an equivalent territory in Germany.