The number of Turkish troops opposing the Bulgarians in Thrace was about 180,000, and they had almost exactly the same number wherewith to oppose the Serbians in Macedonia; for, although Macedonia was considered by the Turks to be the most important theatre of war, yet the proximity of the Bulgarian frontier to Constantinople made it necessary to retain a large number of troops in Thrace. On October 19 the Bulgarians took the frontier town of Mustafa Pasha. On October 24 they defeated the Turks at Kirk-Kilisse (or Lozengrad), further east. From October 28 to November 2 raged the terrific battle of Lule-Burgas, which resulted in a complete and brilliant victory of the Bulgarians over the Turks. The defeat and humiliation of the Turks was as rapid and thorough in Thrace as it had been in Macedonia, and by the middle of November the remains of the Turkish army were entrenched behind the impregnable lines of Chataldja, while a large garrison was shut up in Adrianople, which had been invested by the end of October. The Bulgarian army, somewhat exhausted by this brilliant and lightning campaign, refrained from storming the lines of Chataldja, an operation which could not fail to involve losses such as the Bulgarian nation was scarcely in a position to bear, and on December 3 the armistice was signed. The negotiations conducted in London for two months led, however, to no result, and on February 3, 1913, hostilities were resumed. These, for the Bulgarians, resolved themselves into the more energetic prosecution of the siege of Adrianople, which had not been raised during the armistice. To their assistance Serbia, being able to spare troops from Macedonia, sent 50,000 men and a quantity of heavy siege artillery, an arm which the Bulgarians lacked. On March 26, 1913, the fortress surrendered to the allied armies.
The Conference of London, which took place during the spring of that year, fixed the new Turco-Bulgarian boundary by drawing the famous Enos-Midia line, running between these two places situated on the shores respectively of the Aegean and the Black Sea. This delimitation would have given Bulgaria possession of Adrianople. But meanwhile Greece and especially Serbia, which latter country had been compelled to withdraw from the Adriatic coast by Austria, and was further precluded from ever returning there by the creation of the independent state of Albania, determined to retain possession of all that part of Macedonia, including the whole valley of the Vardar with its important railway, which they had conquered, and thus secure their common frontier. In May 1913 a military convention was concluded between them, and the Balkan League, the relations between the members of which had been becoming more strained ever since January, finally dissolved. Bulgaria, outraged by this callous disregard of the agreements as to the partition of Macedonia signed a year previously by itself and its ex-allies, did not wait for the result of the arbitration which was actually proceeding in Russia, but in an access of indignation rushed to arms.