Theconvention of Sofia betweenBulgaria and theOttoman Empire (Turkey) was signed on 6 September(24 AugustO.S.) 1915. It rectified the border between the two countries in Bulgaria's favour in order to bring Bulgaria into theFirst World War on the side of theCentral Powers.
Adefensive alliance between Bulgaria and Turkey had been concluded on 19 August 1914, but negotiations for Bulgaria's intervention in the war did not begin between the two parties until May 1915. It quickly became clear that Bulgaria sought a rectification of the border, andGermany andAustria-Hungary put pressure on their Ottoman ally to accept.[1] The Austro-Hungarians for their part were convinced that a Turco-Bulgarian alliance would keepGreece andRomania neutral. The German ambassador to Turkey,Hans von Wangenheim, was unconvinced by the proposed alliance, believing that Romanian neutrality could only be secured by Austro-Hungarian territorial concessions. The Austro-Hungarian ambassador,Johann von Pallavicini, convinced the Ottomans to accept a border rectification, but Bulgaria initially refused to consider abandoning their neutrality—the only condition on which the Ottomans would yield territory.[2]
On 6 August 1915, the British launchedan offensive on Gallipoli that exposed Turkey's grave shortage of munitions. On 17 August, the Turkish minister of war,Enver Pasha, wrote to the German chief of staff,Erich von Falkenhayn, to see if an Austro-German offensive againstSerbia was forthcoming. When told that it hinged on Bulgaria's intervention, which in turn hinged on a Turco-Bulgarian pact, the Ottomans reached a quick agreement with Bulgaria on 22 August.[2] They ceded theMaritsa river and its left bank to a depth of 1.5 kilometres.[3] This gave Bulgaria control of the railway to theAegean port ofDedeagach.[4] It also leftEdirne (Adrianople) vulnerable to Bulgarian attack, but signature of the accord was dependent on a military convention being signed between Bulgaria, Austria-Hungary and Germany.[2]
In addition to the Bulgarian-Ottoman convention, Bulgaria also signed atreaty of alliance with Germany and a military convention between Germany, Austria-Hungary and Bulgaria inSofia on 6 September. Bulgaria agreed to allow the transit of German and Austro-Hungarian supplies through its territory to the Ottoman Empire and to invade Serbia with a large force.[2] By November, Turkey's critical supply problem, which had threatened to destroy the regime in August, had been resolved.[5]
