The Congress of Berlin (13 June - 13 July 1878) was a meeting of the European Great Powers' and the Ottoman Empire's leading statesmen in Berlin in 1878. In the wake of the Russo-Turkish War of 1877 78, the meeting's aim was to reorganize the countries of the Balkans. Otto von Bismarck, who led the Congress, undertook to balance the distinct interests of the United Kingdom, Russia and Austria-Hungary. As a consequence, however, differences between Russia and Austria-Hungary intensified, as did the nationality question in the Balkans. The congress was aimed at the revision of the Treaty of San Stefano and at keeping Constantinople in Ottoman hands. It effectively disavowed Russia's victory over the decaying Ottoman Empire in the Russo-Turkish War. The Congress of Berlin returned to the Ottoman Empire territories that the previous treaty had given to the Principality of Bulgaria, most notably Macedonia. The congress formally recognized the independence of the de facto sovereign states of Montenegro, Serbia and Romania, as the 27th-29th free states of the world.