Alliance treaty signed in Sofia

On 6 September 1915, or 24 August by the Julian calendar then used in Bulgaria, Prime Minister Vasil Radoslavov and the German minister in Sofia, Gustav Michahelles, signed a treaty of friendship and alliance between Bulgaria and Germany. On the same day a secret agreement setting out Bulgaria’s reward for taking part in the war was concluded, together with a military convention on a joint attack on Serbia. After a year of manoeuvring between the two sides, Sofia bound itself to the Central Powers. Everything took place in the strictest secrecy, and for several more weeks the Entente went on courting Bulgaria, unaware that it had already lost it.

A British chronology of the war places the alliance treaty in Sofia under 17 July 1915 and adds that in return for taking part in the war Bulgaria was to receive Albania. Both statements are wrong. In mid-July the Central Powers were still only courting Sofia. Around 17–18 July Prince Ernst zu Hohenlohe-Langenburg passed through the Bulgarian capital on his way to Constantinople, where he had been sent to stand in for the ailing ambassador. The Italian minister in Sofia reported that Tsar Ferdinand received him in a long audience, and the Bulgarian press supposed that the talks concerned an agreement with Turkey. Albania was not the subject of the September agreements. The price of Bulgaria’s accession was Serbian Macedonia.

Three documents

The treaty of alliance had five articles and was to remain in force for five years. The parties undertook not to conclude alliances directed against each other. Germany guaranteed Bulgaria’s independence and territorial integrity against any unprovoked attack. Bulgaria was to come to Germany’s aid if it were attacked without cause by one of the neighbouring states. The treaty was to remain secret until Bulgaria entered the war.

The most important document was the secret agreement annexed to the treaty. In it Germany guaranteed Bulgaria the whole Serbian part of Macedonia, including the so-called contested and uncontested zones of the Bulgarian–Serbian agreement of 1912, as well as the Serbian lands east of the Morava, with the valley of the Timok. If Romania entered the war against Bulgaria or its allies, Bulgaria could recover the Dobruja lost in 1913. If Greece did so, Bulgaria could take from it the lands won in the Second Balkan War, including Kavala. Germany and Austria-Hungary granted Bulgaria a war loan of 200 million francs, with the promise of more money if the war lasted longer than four months.

The third document was the military convention, signed not in Sofia but at German headquarters in Pless. It was signed by the chiefs of the general staff of Germany and Austria-Hungary, Erich von Falkenhayn and Franz Conrad von Hötzendorf, and for Bulgaria by Petar Ganchev, formerly military attaché in Berlin. Germany and Austria-Hungary were to attack Serbia within 30 days with at least six divisions, and Bulgaria within 35 days with at least four, and also to send one more division to Macedonia. Field Marshal August von Mackensen was to be in overall command. The aim was to crush the Serbian army and open as quickly as possible an overland route from Hungary through Bulgaria to Turkey. Towards Greece and Romania Bulgaria was to remain neutral as long as they remained neutral.

The agreement with Turkey

Turkey finally agreed to cede to Bulgaria a strip of land along the Maritsa, with the Edirne railway station at Karaağaç and the town of Didymoteicho (PL), about 2,600 square kilometres in all. The railway to the Aegean port of Dedeagach (PL) now ran entirely through Bulgarian territory. The Turks had long resisted, but gave way under German pressure and in the face of the threat at the Dardanelles. Bulgarian sources date the convention to 6 September. The British chronology records its signature at Didymoteicho on 9 September, and the conclusion of a further agreement on the matter on 22 September.

The end of the contest for Bulgaria

For a whole year the Entente and the Central Powers had been bidding for Sofia. Before the war Bulgaria had already taken a large loan in Germany, but Radoslavov and the Tsar long avoided committing themselves finally to either side. The Entente promised the Bulgarians eastern Thrace up to the Enos–Midia line and part of Macedonia, but it could not force Serbia and Greece to give up the lands they had won in 1913. The Central Powers could promise more, because they were paying at others’ expense. Events at the fronts also decided the choice. In the summer the Russians were retreating from Galicia and Poland, and the Allies were stuck at Gallipoli.

On 21 and 22 September Bulgaria announced mobilisation, while the Entente ministers in Sofia were still trying to persuade it to change its mind. At the beginning of October Germany and Austria-Hungary struck at Serbia from the north, and in mid-month the Bulgarians attacked it from the east. By the end of the year Serbia had been conquered and its army had retreated across the Albanian mountains to the Adriatic.