With the Treaty of London the definitive departure of the Ottoman Turks from the European territories of the Empire was ensured. The issue of the distribution of these territories among the allied ( so-far) Balkan states remained open however.

On the Greek side, Lambros Koromilas had proposed the international control of the area of the Straits and Constantinople, the grant of western Thrace (between the Rivers Nestos and Evros) to Bulgaria, and the area of Macedonia between Kavala, Thessaloniki and as far as Avlona on the shores of the Adriatic Sea, to Greece. Bulgaria demanded the implementation of the terms of the Treaty of San Stephano, it claimed, that is, the whole of Macedonia as far as Monastir. It was evident that under these conditions no understanding would be feasible. At the same time, Bulgaria had strong disputes with Serbia concerning the distribution of northern Macedonia that had been captured by the Serbian army.

These facts led to the formation of a common Greco-Serbian front against Bulgaria, ratified with friendship and a mutual protection treaty between Greece and Serbia, signed in Thessaloniki on 19 May/1 June 1913. According to this treaty, the borders of the two countries were defined (similar to the present ones) recognizing essentially the fait accompli caused by the occupation of territories by the two armies, but commercial facilities were provided to the Serbs in the port of Thessaloniki. Next, the claims of the two countries on Bulgaria were outlined, to be resolved through international arbitration. In the event of the latter's refusal to consent to such a perspective, a clash would be inevitable.

The Treaty only exacerbated the crisis. On 17/30 June 1913 Bulgarian forces attacked the Greek and Serbian positions in Macedonia. On that same day the Greek side demanded the evacuation of Thessaloniki by the Bulgarian garrison that had been stationed there since October. The refusal led to clashes within the city, leaving several dead and ending in the capture of the whole Bulgarian military force. There followed the Battles of Kilkis-Lachanas and Doirani, in which Greek troops were victorious, a fact that allowed the capture of Kilkis, Drama and Serres by the Greek army, while forces of the Greek Navy captured Kavala and were forwarded to western Thrace. On 18 July an armistice was signed that found the Bulgarian troops at a disadvantage. The final arrangements came about with the Treaty of Bucharest.