The Greek–Serbian Treaty of Alliance is signed, paving the way for the Second Balkan War.

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.

The Second Balkan War was a conflict fought between Bulgaria and its former Balkan League allies, Serbia and Greece, who were later joined by Romania and the Ottoman Empire. The war began when Bulgaria, unhappy with the division of territory after the First Balkan War, launched attacks on Serbian and Greek forces, who repelled the offensive and pushed into Bulgarian territory. With most of Bulgaria’s army committed in the south, Romania intervened from the north. The Ottoman Empire also took advantage of the situation to recover territories lost the previous year.