The Balkan Wars were two conflicts that took place in the Balkan states in 1912 and 1913. In the First Balkan War, the four Balkan states of Greece, Serbia, Montenegro and Bulgaria declared war upon the Ottoman Empire and defeated it, in the process stripping the Ottomans of their European provinces, leaving only Eastern Thrace under Ottoman control. In the Second Balkan War, Bulgaria fought against the other four combatants of the first war. It also faced an attack from Romania from the north. The Ottoman Empire lost the bulk of its territory in Europe. Although not involved as a combatant, Austria-Hungary became relatively weaker as a much enlarged Serbia pushed for union of the South Slavic peoples. The war set the stage for the July crisis of 1914 and as 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. Over the course of the Macedonian Struggle these states fought for influence between themselves and the Ottoman government within Ottoman Macedonia, during which their governments came under the control of nationalists. In 1912, these countries united to formed the Balkan League. The First Balkan War began on 8 October 1912, when the League member states attacked the Ottoman Empire, and ended eight months later with the signing on 30 May 1913 of the Treaty of London negotiated together with the Great Powers. The Great Powers - particularly Italy and Austria-Hungary -- included independence for Albania in the Treaty. The Second Balkan War began on 16 June 1913, when Bulgaria, dissatisfied with its allotment of territory from Macedonia, attacked its former Balkan League allies. The combined forces of the Serbian and Greek armies, with their superior numbers repelled the Bulgarian offensive and counter-attacked by invading Bulgaria from the west and the south. Romania, having taken no part in the first conflict, had intact armies to strike with and invaded Bulgaria from the north in violation of a peace treaty between the two states. The Ottoman Empire also attacked Bulgaria and advanced in Thrace, regaining Adrianople. In the resulting Treaty of Bucharest, Bulgaria managed to retain most of the territories it had gained in the First Balkan War. However, it was forced to cede the ex-Ottoman south part of Dobruja province to Romania.