The Balkan Wars were two conflicts that took place in the Balkan Peninsula in south-eastern Europe 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." By the early 20th century, Bulgaria, Greece, Montenegro and Serbia had achieved independence from the Ottoman Empire, but large elements of their ethnic populations remained under Ottoman rule. In 1912, these countries formed the Balkan League. There were three main causes of the First Balkan War. The Ottoman Empire was unable to reform itself, govern satisfactorily, or deal with the rising ethnic nationalism of its diverse peoples. Secondly the Great Powers quarreled amongst themselves and failed to ensure that the Ottomans would carry out the needed reforms. This led the Balkan states to impose their own solution. Most important, the Balkan League had been formed, and its members were confident that it could defeat the Turks.