A conference held to negotiate the peace after the Crimean War, attended by Britain, Austria, Russia, Turkey, and Sardinia. It marked a defeat for Russia, which conceded part of Bessarabia to Moldavia and Wallachia in the Balkans. The revival of the Straits Convention of 1841 meant that the Black Sea was again closed to all warships and neutralized while navigation of the Danube was to be free. The Ottoman empire was placed under joint guarantee of the West European powers and the sultan agreed to recognize the rights of his Christians. The decline of the Ottoman empire, however, was not halted and Russia, determined to retrieve its Balkan supremacy, was to break the Black Sea clause in 1870.