The heterogeneous composition of the Austrian Empire, which demanded a strictly conservative policy at home, prescribed no less urgently the preservation of peaceful relations abroad. Since the conclusion of the great war Metternich's foreign policy had had no other object than the maintenance of the _status quo_, by the strict observation of existing treaties. The revolutionary spirit was the most serious danger to the settlement of 1815. Bonaparte might be dead or a prisoner at St. Helena, but Metternich was under no illusion that the peril had passed away for ever. The revolutionary monster still survived and required ceaseless watching. Only, he conceived, by a European Confederation, ruled over by a council of the Great Powers, could complete security be obtained against the common enemy of all established governments. Metternich's combination of the Powers "for the maintenance of everything lawfully existing,"[17] which has been held up to execration under the name of the Holy Alliance, was an adaptation to practical politics of the fantastic scheme, which Alexander had propounded, on September 26, 1815, after a review of his army on the plain of Vertus. According to the Tsar's manifesto the relations of all European sovereigns were in the future to be guided by the teachings of Christ. They were to regard each other in the light of brothers and to look upon their subjects as their children. The policy of Metternich's Holy Alliance was set forth in the famous preliminary protocol of the conference of Troppau, signed, on November 19, 1820, by the plenipotentiaries of Austria, Russia, and Prussia. "States," it was laid down, "which have undergone a change of government due to a revolution, the results of which affect other States, shall cease to be members of the European Alliance. If owing to these alterations immediate danger threaten neighbouring States, the Powers bind themselves to bring back by force of arms the erring State into the folds of the Alliance."