The final in a series of wars between Russia and the Ottoman Empire, beginning in the early 18th century.
The Russo-Turkish War of 1877-1878 began in 1875 with an uprising in Bosnia and Hercegovina against the Ottomans. Russia, always meddling in Balkan politics, instigated additional risings in Serbia and Montenegro. As the Ottoman Empire fought to put down the rebels, Russian diplomats worked to ensure Austrian neutrality in the coming conflict.
Once Austria had agreed to stay out of the war, Russia declared its entry into the war, on the side of the rebels (1877). The war, already going badly for the Ottomans, turned even worse.
After a year of fighting, the Treaty of San Stefano (1878) put an end to the war, and finally broke the Ottoman hold on the Balkans. By the terms of the treaty, the Ottoman Empire ceded the Dobruja and part of Armenia to Russia, and recognised the independence of Romania, Serbia and Montenegro. The latter two were also substantially enlarged in territory. Furthermore, Bulgaria became autonomous.
Because of the sudden growth in Russian influence in the Balkans, however, the other European major powers were unhappy with the Treaty of San Stefano. Citing the terms of the Treaty of Paris (1856), they called a conference (the Congress of Berlin) to revise the treaty.
The Congress produced major revisions to the terms agreed at San Stefano. Bulgaria was divided into three states, with varying degrees of autonomy; Romania was forced to trade part of Bessarabia to Russia in return for the Dobruja; Bosnia and Hercegovina, over whose independence the war had been fought, became military protectorates of Austria-Hungary. The Congress also assigned Cyprus as a British protectorate, and delivered further territories in Asia from Turkish to Russian control.
As a result of the Congress, Russia's informal alliance (The Three Emperors' League) with Germany and Austria-Hungary was weakened, though it continued to exist until 1887, in drastically weakened form.