From these proceedings Prussia and Austria held rigorously aloof. Both had signed the protocol of 1852, and both realized that, if the European powers were to be given no excuse to intervene, their attitude must be scrupulously "correct"; and this involved the recognition of King Christian's rights in the duchies. On the other hand, the constitution of the 13th of November had been in flat contradiction to the protocol of London, which recognized the separate rights of the duchies; and if the two great German powers chose to make this violation of an agreement to which they had been parties a _casus belli_, Europe would have no right to interfere. Prussia had begun to mobilize in November; and Austria also soon realized that action must speedily be taken if the lesser German governments were not to be allowed to get out of hand. Russia and Great Britain had already protested against the occupation of Holstein and the support given to the Augustenburg claimant; and now Beust, the Saxon minister, was proposing that the federal diet, which had been no party to the protocol, should formally recognize his claim. Bismarck, then, had no difficult task in persuading Austria that the time for action had come. A last attempt of the two powers to carry the diet with them in recognizing the protocol having failed, they formally announced that they would act in the matter as independent European powers. On the 16th of January 1864 the agreement between them was signed, an article, drafted by Austria, intended to safeguard the settlement of 1852, being replaced at the instance of Prussia by another, which stated that the contracting powers would decide only in concert upon the relations of the duchies, and that in no case would they determine the succession save by mutual consent. A clause was also inserted provisionally recognizing the principle of the integrity of Denmark. Danish War of 1864.