A defensive 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, and Germany and Austria-Hungary put pressure on their Ottoman ally to accept. The Austro-Hungarians for their part were convinced that a Turco-Bulgarian alliance would keep Greece and Romania 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.
