The Greek–Serbian Alliance of 1913 was signed at Thessaloniki on 1 June 1913, in the aftermath of the First Balkan War, when both countries wanted to preserve their gains in Macedonia from Bulgarian expansionism. The treaty formed the cornerstone of Greek–Serbian relations for a decade, remaining in force through World War I until 1924. Background During the First Balkan War, both Greek and Serbian armies concluded their operations in Macedonia by late 1912, while the Bulgarian army was directed mainly towards Thrace. As a result, the former succeeded in taking control of most of Macedonia, including its largest city, Thessaloniki, which was occupied by the Greek army in early November. Bulgaria nevertheless demanded most of Macedonia for herself, relying on the crucial role its army had played in facing the bulk of the Ottoman army in the First Balkan War, as well as on the pre-war agreements with Serbia regarding their mutual territorial claims in northern Macedonia. Both Greece, which had not signed any agreement on territorial partition, and Serbia, which in the London Conference of 1912–13 was forced by the Great Powers to cede its conquests in Albania in favour of the newly created Albanian Principality, opposed Bulgarian claims and insisted on an uti possidetis division of territory. Negotiations and signing of the alliance On 9 March 1913, the Greek Foreign Minister Lambros Koromilas instructed the Greek ambassador to Belgrade to sound out the Serbian government with a view to a bilateral alliance treaty. Preliminary discussions quickly bore fruit, and on 5 May Koromilas and the Serbian ambassador to Athens signed the first protocol, where both sides pledged mutual support against Bulgaria should the latter refuse to acknowledge the territorial status quo. The protocol also included a 50-year commercial agreement which allowed the use of Thessaloniki by Serbian companies. This protocol was then followed by a military convention signed on 13 May at Thessaloniki. The Serbian government however refused to ratify the latter, insisting that Greece take on itself the previous Bulgarian pledge to provide 200,000 troops in the case of an Austrian attack. The Greek government was reluctant to agree to this, but following the clashes between Greek and Bulgarian troops among the mutual demarcation line at Nigrita and Mount Pangaion, as well as the view of Prime Minister Eleftherios Venizelos that an Austro-Serbian war would soon draw the other Great Powers into the fray, it agreed. The