End of the Austro-Prussian understanding.
Napoleon having been successfully hoodwinked, Bismarck turned to Italy. His previous advances had been interrupted by the Gastein convention, which seemed to the Italian government a betrayal of the Italian cause. Italy attempted to negotiate with Austria for the purchase of Venetia; but the offer was curtly refused by the emperor Francis Joseph, and the counter-proposal of a commercial _rapprochement_ was forestalled by Prussia, which with the aid of most of the lesser states, angered by the betrayal of their interests by Austria at Gastein, arranged a commercial treaty between Italy and the Zollverein, an act which involved the recognition of the Italian kingdom. The counter-stroke of Austria was to embarrass Prussia by allowing full play in Holstein to the agitation in favour of the Augustenburg claimant. To the protests of Prussia, Austria replied that she had a full right to do what she liked in the duchy, and that she still adhered to the declaration of the princes, made on the 28th of May 1864, in favour of Duke Frederick. This "perfidy" removed the last scruples of King William; and the Austro-Prussian alliance came to an end with the declaration of Bismarck that Prussia "must win full freedom for her own entire policy" and his refusal to continue the correspondence.
War, though still postponed, was now certain; and with this certainty the desire of the Italians for the Prussian alliance, now recommended by Napoleon, revived. By the 16th of March 1866 the Austrian war preparations were so far advanced that Count Mensdorff thought it safe to send an ultimatum to Prussia and, at the same time, a circular note to the princes declaring that, in the event of an evasive reply, Austria would move in the diet for the mobilization of the federal forces. On the 24th Bismarck in his turn issued a circular note stating that, in view of the Austrian war preparations, Prussia must take measures for her defence; at the same time he laid before the princes the outline of the Prussian scheme for the reform of the Confederation, a scheme which included a national parliament to be elected by universal suffrage, "as offering surer guarantees for conservative action than limitations that seek to determine the majority beforehand." Clearly Prussia meant war, and the Italian government thought it safe to sign, on the 8th of April 1866, a treaty of alliance. By this instrument it was agreed that in the event of her proposals for the reform of the federal constitution being rejected by the German princes, Prussia should declare war "in order to give effect to her proposals," and that, in that case, Italy would also declare war against Austria. As a result of the war Venetia was to be added to Italy and an equivalent amount of territory in North Germany to Prussia. The agreement, however, was only to hold good if war broke out within three months.