The Russo-Turkish War of 1877-1878 had its origins in the Russian goal of liberating the Slav peoples of the Balkan Peninsula of south-eastern Europe from the Turkish-ruled Ottoman Empire and dominating Istanbul (Constantinople) and the adjacent Turkish Straits.
After an anti-Ottoman uprising in Bosnia and Herzegovina in the summer of 1875, the formal pretext for the war came with the atrocities committed against the civilian Slav population during the Bulgarian April uprising of 1876. The Balkan principalities of Serbia and Montentgro declared war against their nominal Ottoman overlord early in July 1876, Russia following suit (24 April 1877) after the failure of peace negotiations over the winter.
The ensuing campaign ended in resounding victory for the Russian army, supported by a Romanian corps and volunteer brigades from the local Bulgarian population. Among the highlights of the campaign were the siege (July-December 1877) and subsequent surrender of the Turkish troops at Pleven and the battles at the Stara Planina mountain passes waged, especially at Shipka, to prevent reinforcements from reaching Pleven.
In February 1878 the Russian army had almost reached Istanbul, but scared the city might fall, the British sent a fleet of ships. Under negotiating "help" from that fleet and the fact that the Russians had suffered such enormous losses (by some estimates about 200,000 men) Russia settled for the highly advantageous Treaty of San Stefano (March 3), only to later see her diplomatic gains largely dismantled (July 13) in the Treaty of Berlin, 1878.