text: In the long-run, tensions 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, thus setting up a strong revanchist demand in Bulgaria that in 1912 was one of many causes of the First Balkan War.
  20th century
  Balkan Wars
  The Balkan Wars were two wars that took place in the Balkans in 1912 and 1913. Four Balkan states defeated the Ottoman Empire in the first war; one of the four, Bulgaria, was defeated in the second war. The Ottoman Empire lost nearly all of its holdings in Europe. Austria-Hungary, although not a combatant, was weakened as a much enlarged Serbia pushed for union of the South Slavic peoples.  The war set the stage for the Balkan crisis of 1914 and thus was a "prelude to the First World War."
  World War I
  Coming of war in 1914
  World War I was ignited from a spark in the Balkans, when a Bosnian Serb named Gavrilo Princip assassinated the heir to the Austrian throne, Franz Ferdinand. Princip was a member of a Serbian secret military society called the Crna Ruka (Serbian for "Black Hand"). Following the assassination, Austria-Hungary sent Serbia an ultimatum in July 1914 with several provisions largely designed to prevent Serbian compliance. When Serbia only partially fulfilled the terms of the ultimatum, Austria-Hungary declared war on Serbia on 28 July 1914.