|Tsar Ferdinand of Bulgaria and King Peter of Serbia|
The heavy-handed policies in Macedonia of the Young Turks regime (which had come to dominate the declining Ottoman Empire in 1908) and the outbreak of the Turko-Italian War in September 1911 energized—in all the Balkan countries simultaneously—an impulse toward joint action against Turkey. In late 1911, secret negotiations started among Bulgaria, Serbia, Greece, and Montenegro with the objective of expelling the Ottomans from European territory. The most important connection was between Bulgaria and Serbia. A treaty of alliance signed by the ministers and monarchs of both kingdoms was executed on 12 March 1912. There were two parts to the Bulgar-Serbian treaty. One part created a defensive alliance between the contracting parties, in which they pledged themselves to "succor one another with their entire forces in the event of one of them being attacked by one or more States." The other part is the "secret annex," in which they provided for possible war against Turkey, in the event of internal or external troubles of Turkey which might endanger the national interests of either of the contracting parties or threaten the maintenance of the status quo in the Balkan peninsula.
This alliance led to military conventions and the formation of a "Balkan Alliance." The first of two Balkan Wars was launched by the Alliance in October and succeeded in expelling the Turks from all Europe except the Constantinople region. The two Balkan Wars of 1912–1913 placed enormous stress on the diplomatic system of the great powers, gave great impetus to Serbia's annexation ambitions, and alarmed Austria-Hungary.
View the treaty and and its secret appendix HERE