Peace negotiations were held in Bucharest, Romania, which were attended by Bulgaria, Romania, Serbia, Montenegro, and Greece. The talks led to the Treaty of Bucharest, signed on August 10, 1913, which ended the state of war between the signatories. Bulgaria and the Ottoman Empire negotiated separately, producing the Treaty of Constantinople, signed on September 29, 1913, which also ended hostilities between the two countries.
As a result of these treaties, Bulgaria lost most of the lands it had won in the First Balkan War, including most of Macedonia (to Serbia and Greece) and Eastern Thrace (to the Ottoman Empire); it also ceded Southern Dobruja to Romania. Bulgaria did retain a portion of Macedonia and Western Thrace, including an outlet to the Aegean Sea through Dedeagach. Bulgaria’s participation in the two Balkan Wars netted her a 16% gain in territory. By contrast, the victors in both Balkan Wars made much larger gains: Montenegro (62%), Greece (68%), and Serbia (nearly 100%). Romania gained 5%. However, the Ottoman Empire lost nearly all of Rumelia (its last European possession), retaining only Eastern Thrace.
(Taken from Second Balkan War – Wars of the 20th Century – Vol. 3)
Background The First Balkan War (previous article) allowed the Balkan League (Serbia, Bulgaria, Greece, and Montenegro) to gain control of nearly the whole region of Rumelia. Then in the 1913 Treaty of London, the major European powers recognized the independence of Albania, forcing Serbia, Greece, and Montenegro to withdraw their forces from their respective conquered territories in Albania. Before the war, Serbia and Bulgaria had entered into a secret agreement to partition Rumelia between them, in particular the Macedonian region. No similar partition agreement was made with Greece, as the Greek Army was not highly regarded and thought to be incapable of gaining much territory.
During the war, however, Bulgaria had concentrated much of its military resources in Eastern Thrace aiming to capture Constantinople, and left a much smaller force to invade Macedonia. As a result, Bulgaria’s allies, Serbia and Greece, both of whom faced much less opposition in their sectors, gained considerable territory during the war. Serbian forces advanced into southern Macedonia past the so-called “disputed zone” north of the Kriva Palanka-Ohrid Line, which was part of the Serbian-Bulgarian pre-war partition agreement. The Greek Army also performed (surprisingly) well and seized a large section of southern Macedonia and portions of Western Thrace.
The Bulgarians applied pressure on Serbia to withdraw its forces to the north and beyond Monastir in compliance with their pre-war arrangement. Serbia refused, as it already had been forced to relinquish northern Albania, while Bulgaria had ceded much less in Eastern Thrace, in the areas of the Enos-Midia Line. Serbia insisted that new negotiations be started on partitioning Macedonia, a proposal that was rejected by Bulgaria. (In their pre-war agreement, Serbia was allowed to expand freely into Albania, while Bulgaria could take southern Macedonia.)
Bulgaria also put pressure on Greece to withdraw from Western Thrace and southern Macedonia, in particular from Thessalonica. The Greeks offered a compromise agreement, which the Bulgarians rejected. Then as Bulgaria continued its war posturing and increased its forces in the disputed areas, on June 1, 1913, Serbia and Greece secretly signed a mutual defense treaty aimed at countering a potential Bulgarian attack. The agreement also fixed a common border between Serbia and Greece. Consequently, small-scale fighting began to break out between Serbians and Bulgarians, whose forces were situated next to each other following the recently concluded First Balkan War. A small Montenegrin contingent also joined ranks with Serbian forces.
Meanwhile, Russia was alarmed at the impending break up of the Serbian-Bulgarian alliance, as this threatened Russia’s power ambitions in the Balkan region. Tsar Nicholas II, the Russian monarch, offered to mediate, even sending a personal letter to both the Serbian and Bulgarian kings. Bulgaria was unyielding, however, forcing the Russian government to cancel the Russo-Bulgarian Treaty of 1902.