The Vardar offensive () was a World War I military operation, fought between 15 and 29 September 1918. The operation took place during the final stage of the Balkans Campaign. On September 15, a combined force of Serbian, French and Greek troops attacked the Bulgarian-held trenches in Dobro Pole ("Good Field"), at the time part of Serbia (present-day North Macedonia). The assault and the preceding artillery preparation had devastating effects on Bulgarian morale, eventually leading to mass desertions. On September 18, a second Entente formation assaulted the Bulgarian positions in the vicinity of Lake Doiran. Effectively employing machine gun and artillery fire the Bulgarians managed to stall the Allied advance on the Doiran sector. However the collapse of the front at Dobro Pole forced the Bulgarians to withdraw from Doiran. The Allies pursued the German 11th Army and the Bulgarian 1st Army, while pushing deeper into Vardar Macedonia. By 29 September, the Allies had captured the former HQ of Skopje, thus endangering the remnants of the 11th Army. The parallel development of the anti-monarchist Radomir Rebellion forced Bulgaria to sign the Armistice of Salonica and withdraw from the war. The treaty included the full capitulation of the 11th Army, bringing the final tally of Bulgarian and German prisoners to 77,000 and granting the Allies 500 artillery pieces. The Bulgarian downfall turned the strategic and operational balance of the war against the Central Powers. The Macedonian Front was brought to an end at noon on 30 September, when the ceasefire came into effect. Prelude The 28 June 1914, assassination of Austro-Hungarian heir presumptive Archduke Franz Ferdinand precipitated Austria-Hungary's declaration of war against Serbia. The conflict quickly attracted the involvement of all major European countries, pitting the Central Powers against the Entente coalition and starting World War I. Serbia was defeated during the autumn 1915 phase of the Serbian Campaign, prompting France and Britain to transfer troops from the Gallipoli Campaign to Greek Macedonia. The Macedonian front was thus established in an effort to support the remnants of the Serbian army to conquer Vardar Macedonia. On 17 August 1916, in the Struma offensive Bulgaria invaded Greece, easily conquering all Greek territory east of the Struma, since the Greek Army was ordered not to resist by the pro-German King Constantine. The surrender of territory recently won with difficulty in the Second Balkan War of 1913 was the last straw for many supporters of