Two wars in South-eastern Europe in 1912-1913 in the couse of which the Balkan League (Serbia, Montenegro, Greece and Bulgaria) first conquered Ottoman-held Macedonia and most of Thrace and then fell out over the division of the spoils, Bulgaria suffering defeat at the hands of her former allies and losing much of what she had been promised in the initial partition scheme.
The wars were an important precursor to World War I, to the extent that Austria-Hungary took alarm at the great increase in Serbia's territory and regional status. This concern was shared by Germany, which saw Serbia as a satellite of Russia. Serbia's rise in power thus contributed to the two Central Powers' willingness to risk war following the assassination of the Austrian Archduke Francis Ferdinand in Sarajevo in June 1914.
The background to the wars lies in the incomplete emergence of nation-states on the fringes of the Ottoman Empire during the nineteenth century. Serbia had gained substantial territory during the Russo-Turkish War of 1877-1878, while Greece acquired Thessaly in 1881 (although she lost a small area to Turkey in 1897) and Bulgaria (an autonomous principality since 1878) incorporated the formerly distinct provinvce of Eastern Rumelia (1885). All three as well as tiny Montenegro sought additional territories within the large Turkish-ruled regions known as Albania, Macedonia and Thrace.
Tensions among the Balkan states over their rival aspirations in Macedonia subsided somewhat following intervention by the great powers in the mid-1900s aimed at securing fuller protection for the province's Christian majority. The question of Ottoman rule's viability revived, however, after the Young Turk revolution of July 1908 compelled the Sultan to restore the suspended Ottoman constitution.
While Austria-Hungary seized the opportunity of the resulting Ottoman political uncertainty to annex the formally Ottoman province of Bosnia-Herzegavina, which it had occupied since 1878, Bulgaria declared itself a fully independent kingdom (October 1908) and the Greeks of Crete proclaimed unification with Greece, though the opposition of the great powers prevented the latter action from taking practical effect.
Frustrated in the north by Austria-Hungary's incorporation of Bosnia with its minority of half a million Serbs, and forced (March 1909) to accept the annexation and restrain anti-Habsburg agitation among Serbian nationalist groups, the Serbian government looked to the formerly Serb territories in the south, notably "Old Serbia" now mostly the province of Kosovo).
On August 28, 1909, demonstrating Greek officers urging constitutional revision and a more nationalist foreign policy secured the appointment of a more sympathetic government which they hoped would resolve the Cretan issue in Greece's favour and reverse the defeat of 1897. Bulgaria, which had secured Ottoman recognition of her independence in April 1909 and enjoyed the friendship of Russia, also looked to districts of Ottoman Thrace and north-eastern Macedonia for expansion. In August 1910 Montenegro followed Bulgaria's precedent by becoming a kingdom.