During the First and Second Balkan Wars of 1912-1913, Bulgaria and other states finally broke the Ottoman Empire’s frail grip over the Balkans. In both conflicts, the Ottomans fought against Bulgaria, and atrocities were committed by each side. Just over 2 years later, the Ottomans and Bulgarians were fighting on the same side during the First World War. My question is, what were Ottoman-Bulgarian relations like during the war? Did they markedly improve? Were grudges still held? How did they overcome them and fight as co-belligerents?
Besides the short fighting in Romania, i don’t believe ottoman/Bulgarian Troops ever worked in tandem, and even then, they where kept separate, Bulgaria had to manage and help oversee Romania and Serbia whilst the ottomans had to focus on things like Gallipoli, the Palestinian front, and the British advance out of Kuwait.
I will mostly talk about the diplomacy in 1914 and so it probably won't satisfy you but i'll try my best. Even though they had been in war before, Sait Halim Pasha (The Grand Vizier) wanted to make an alliance of Ottoman Empire, Bulgaria, and Romania to protect the Empire against a possible another Balkan coalition or attack and to convince the Entente that The Ottomans will remain neutral in the war.
On August 6 1914, one of the conditions that Sait Halim demanded to Wangenheim in return of the activation of secret alliance is for Germany to lend its support to understandings with Romania and Bulgaria, and it will see to it that the Ottomans secures a fair agreement with Bulgaria with reference to possible spoils of war. He also desired that under no circumstances would the Ottomans enter the war on either side before concluding treaty with Romania, Bulgaria, and Greece. On August 9, Talat Pasha under the directions of Sait Halim concluded a treaty with Bulgarian ambassador Radoslavov in Sofia. This treaty was a mutual defense pact that came into effect if either party was attacked by another Balkan power. It was also something of a non-aggression pact, as both parties pledged not to attack other Balkan countries without consultation with each other. In the absence of such consultation, the parties pledged benevolent neutrality in such a conflict. Furthermore, the treaty guaranteed Bulgaria that a bilateral or joint Ottoman-Bulgarian agreement for Romanian neutrality would be negotiated. Bulgaria additionally agreed to notify the Ottomans of any impending military mobilization and to let Ottoman forces to cross Bulgaria to attack another power (possibly Serbia or Greece). The treaty would remain in effect for the duration of the war and it was kept secret from the Germans.
So we could say that during the eve of World War I the relations between the Ottoman Empire and Bulgaria were rather friendly, at least on the surface. During the war the Ottoman General Staff and The Bulgarians coordinated with each other to effectively command and speed up the deployment of their troops in the Galician/Romanian front. The Ottoman and Bulgarian troops were also directly worked together multiple times, especially in Dobruja near the Romanian-Bulgarian frontier