How many countries were members of the Balkan League?

The Balkan League was a quadruple alliance formed by a series of bilateral treaties concluded in 1912 between the Eastern Orthodox kingdoms of Greece, Bulgaria, Serbia and Montenegro, and directed against the Ottoman Empire, which at the time still controlled much of Southeastern Europe.

The League was victorious in the First Balkan War which broke out in October 1912, where it successfully wrestled control of almost all European Ottoman territories. Following this victory however, unresolved prior differences between the allies re-emerged over the division of the spoils, particularly Macedonia, leading to the effective break-up of the League, and soon after, on 16 June 1913, Bulgaria attacked her erstwhile allies, beginning the Second Balkan War.