Jacob Gould Schurman

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.

Tensions among the Balkan states over their rival aspirations to the provinces of Ottoman-occupied Roumelia, namely Eastern Roumelia, Thrace and Macedonia, subsided somewhat following intervention by the Great Powers in the mid-19th century, aimed at securing both fuller protection for the provinces' Christian majority and protection of the status quo. By 1867 Greece, Serbia and Montenegro have all secured their independence, which was confirmed by the Treaty of Berlin a decade later.

But the question of the viability of Ottoman rule was revived after the Young Turk Revolution of July 1908 compelled the Sultan to restore the suspended Ottoman constitution, and the significant developments in the years 1909-1911.

Serbia's aspirations towards Bosnia-Herzegovina were thwarted by the Austrian annexation of the province in October 1908, and so the Serbs focused their attention onto their historic cradle, Kosovo and the south for expansion. Greek officers, revolting in August 1909, had secured the appointment of a progressive government under Eleftherios Venizelos which they hoped would resolve the Cretan issue in Greece's favour and reverse their defeat of 1897 by the Ottomans. 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 Macedonia for expansion. In March 1910, an Albanian insurrection broke out in Kosovo. In August 1910, Montenegro followed Bulgaria's precedent by becoming a kingdom.

In 1911, Italy launched an invasion of Tripolitania, which was quickly followed by the occupation of the Dodecanese Islands. The Italians' decisive military victories over the Ottoman Empire greatly influenced the Balkan states to prepare for war against Turkey. Thus in the spring of 1912, consultations between the various Christian Balkan nations resulted in a network of military alliances which became known as the Balkan League.

The Great Powers, most notably France and Austria-Hungary, reacted to this diplomatic sensation by trying to dissuade the League from going to war, but failed. In late September, both the League and the Ottoman Empire mobilized their armies. Montenegro was the first to declare war, on September 25 (O.S.)/October 8. The other three states, after issuing an impossible ultimatum to the Porte on October 13, declared war on Turkey on October 17.

(Description adapted from Wikipedia)