The Balkan Wars consisted of two conflicts that took place in the Balkan Peninsula in 1912 and 1913. Four Balkan states defeated the Ottoman Empire in the First Balkan War. In the Second Balkan War, Bulgaria fought against all four original combatants of the first war along with facing a surprise attack from Romania from the north. The conflicts ended catastrophically for the Ottoman Empire, which lost the bulk of its territory in Europe. Austria-Hungary, although not a combatant, became relatively weaker 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 served as a "prelude to the First World War".