As New Zealand troops rested on the island of Lemnos in the autumn of 1915, the crisis in the Balkans intensified. By September, Serbia had been fighting alone against Austria-Hungary for more than a year, beating off two invasions with heavy losses. Political and diplomatic events would now conspire against the Serbs.
In the Second Balkan War of 1913, Bulgaria had fought unsuccessfully against its former allies Serbia and Greece in an attempt to increase its share of territory captured by the three states during the First Balkan War against the Ottoman Turks in 1912. The Bulgarians were encouraged by the failure of Britain and France to defeat the Ottomans at Gallipoli. Courted by Germany with offers of Balkan territory, Bulgaria rejected similar French and British approaches. Bulgaria’s entry into the war would open direct overland communication between Germany and the Ottoman Empire.
France, and to a lesser extent Britain, realised that a show of force in the Balkans might be the only way to prevent Bulgaria joining the enemy. The only feasible landing place with sufficient port facilities was the ancient city of Salonika (now Thessaloniki) in the north of neutral Greece. Despite this neutrality, and the sharp political divisions in Greece, the Allies decided to go ahead with this risky pre-emptive action.
The French 156th and British 10th (Irish) divisions (the latter commanded by General Sir Bryan Mahon) began disembarking at Salonika without incident on 5 October 1915; further divisions were en route. German and Austrian troops unleashed a major offensive against the Serbs the following day, and Bulgaria declared war on Serbia a week later. Serbia was now exposed to Bulgarian attack from the east. In late October, the overall commander at Salonika, the politically attuned French General Maurice Sarrail, pushed forces north across the Serbian border to support the Serbian Army, which had finally crumbled and retreated after a brave stand at Kosovo in central Serbia.
With a harsh winter closing in and still largely equipped for a Gallipoli summer, there was little the Anglo-French troops could do to assist the Serbs. The 10th (Irish) Division fought a desperate defensive action against the Bulgars in the snow at Kosturino in December 1915 before the Anglo-French force fell back on Salonika. More than 6000 casualties were suffered during the failed advance into southern Serbia. The remains of the Serbian Army, shattered in battle and suffering from an epidemic of typhus, were forced into a desperate retreat across the mountains into Albania. By the time they arrived at Tirana for evacuation to Corfu by Anglo-French ships, the sick and starving Serbian forces had ceased to exist as a fighting force.
The Allies now had to consider if anything of strategic significance could be achieved in the Balkans, given that Gallipoli was to be evacuated. British commanders favoured withdrawal from Greece to concentrate resources on the Western Front and against the Ottoman Turks in the Middle East. The French, who unlike at Gallipoli were the dominant partner in this campaign, insisted that they should remain, to prevent Greece from being overrun and to maintain an additional front against the Central Powers in southern Europe. To this end, further French troops were already landing at Salonika, and the Army of the Orient (as it was now called) began to fortify defences around the city, wary of both Bulgarian invasion and potential military retaliation by the neutral Greeks.
