The Russo-Turkish War of 1877–1878 (Bulgarian: Руско-турска освободителна война (1877—1878 г.), Russian: Русско-турецкая война (1877—1878 гг.), Ottoman: ۹۳ حربی‎, Doksan Üç Harbi ('93 Harbi, "93 War"), Turkish: '93 Harbi or 1877–78 Osmanlı-Rus Savaşı) was a conflict between the Ottoman Empire and the Eastern Orthodox coalition led by the Russian Empire and composed of numerous Balkan countries. Fought in the Balkans and in the Caucasus, its origins lie in emerging nineteenth-century nationalism in the Balkan region. Additional factors include the Russian aspirations of recovering territorial losses it had suffered during the Crimean War, reestablishing itself in the Black Sea and supporting the political movement attempting to free Balkan nations from the Ottoman Empire.

As a result of the war, Russia succeeded in claiming several provinces in the Caucasus, namely Kars and Batum. The principalities of Romania (which was also forced by Russia to cede the Budjak region of the Danube delta, in spite of an existing treaty of alliance between the two countries), Serbia and Montenegro, each of which had had de facto sovereignty for some time, formally proclaimed independence from the Ottoman Empire. After almost five centuries of Ottoman domination (1396–1878), the Bulgarian state was reestablished as the Principality of Bulgaria, covering the land between the Danube River and the Balkan Mountains (except Northern Dobrudja which was given to Romania) as well as the region of Sofia, which became the new state's capital. The Congress of Berlin also allowed Austria-Hungary to occupy Bosnia and Herzegovina and the United Kingdom to take over Cyprus.