On the basis of British, German, French, and Russian documents, the origins, course, and consequences of the diplomatic struggle between the Russian and Ottoman empires caused by St. Petersburg’s gross interference in international relations in the Balkans have been studied. It is shown that Russia actively, though unsuccessfully, made enormous diplomatic efforts during the First Balkan War of 1912–1913 to persuade the Bulgarian army to relinquish control of Adrianople, which was under Ottoman control at the time because it viewed Bulgaria as its immediate competitor in the potential struggle for control of Constantinople and the Black Sea straits of the Bosporus and the Dardanelles. After all, the capture of these strategically located Ottoman territories was one of the main directions of Russian policy for several centuries. The article considers how the Russian autocracy, on the contrary, already tried to prevent the return of Adrianople to Ottoman control during the Second Balkan War by seeking allies among European powers, no longer wanting to strengthen the sultan’s position near the Bosporus and the Dardanelles, considering these territories as its potential prey. All the tools of St. Petersburg’s pressure on the Ottoman government were analyzed, including threats to carry out a naval operation in the Black Sea Straits or seize part of Turkey’s Asian possessions, and to urge Russia’s ally France to abandon further lending to the Ottoman Empire. It has been proven that such an inconsistent and rather aggressive Russian policy in the Balkans led to the fact that the Ottoman Empire, like Bulgaria, actively sought allies to resist this encroachment, quickly became closer to Germany, and later entered the First World War on its side. It is noted that looking for partners to resist this Russian expansion, the Ottoman government later cooperated quite successfully with the Ukrainian liberation movement, especially the Union for the Liberation of Ukraine, which was represented in Constantinople, and officially declared support for the liberation struggle of the Ukrainian people against tsarist autocracy. Furthermore, it is emphasized that both Russia’s partners in the Entente (France and Great Britain) and its potential rivals in the Triple Alliance (Germany, Austria-Hungary, and Italy) categorically did not accept Russia’s attempts to expand to Ottoman Constantinople, the Bosporus, the Dardanelles and beyond to the Eastern Mediterranean, as it would radically upset the balance of power in Europe and the Middle East and, in general, destabilize international relations to which the great powers were not yet ready.