The Crimean War was fought from October 1853 to February 1856 in which Russia lost to an alliance of the Ottoman Empire, France, the United Kingdom and Piedmont-Sardinia. The immediate cause of the war involved the rights of Christian minorities in Palestine (then part of the Ottoman Empire) with the French promoting the rights of Roman Catholics, and Russia promoting those of the Eastern Orthodox Church. Longer-term causes involved the decline of the Ottoman Empire, the expansion of the Russian Empire in the preceding Russo-Turkish Wars, and the British and French preference to preserve the Ottoman Empire to maintain the balance of power in the Concert of Europe.

In July 1853, Russian troops occupied the Danubian Principalities (now part of Romania but then under Ottoman suzerainty). In October 1853, having obtained promises of support from France and Britain, the Ottomans declared war on Russia. Led by Omar Pasha, the Ottomans fought a strong defensive campaign and stopped the Russian advance at Silistra (now in Bulgaria). Fearing an Ottoman collapse, the British and the French had their fleets enter the Black Sea in January 1854. They moved north to Varna in June 1854 and arrived just in time for the Russians to abandon Silistra.

The allied commanders decided to attack Russia's main naval base in the Black Sea, Sevastopol, on the Crimean Peninsula. After extended preparations, allied forces landed on the peninsula in September 1854. The Russians counterattacked on 25 October in what became the Battle of Balaclava and were repulsed, but the British Army's forces were seriously depleted as a result. A second Russian counterattack, at Inkerman (November 1854), ended in a stalemate as well. The front settled into the siege of Sevastopol, involving brutal conditions for troops on both sides.

Sevastopol finally fell after eleven months, after the French had assaulted Fort Malakoff. Isolated and facing a bleak prospect of invasion by the West if the war continued, Russia sued for peace in March 1856. France and Britain welcomed the development, owing to the conflict's domestic unpopularity. The Treaty of Paris, signed on 30 March 1856, ended the war. It forbade Russia from basing warships in the Black Sea. The Ottoman vassal states of Wallachia and Moldavia became largely independent. Christians in the Ottoman Empire gained a degree of official equality, and the Orthodox Church regained control of the Christian churches in dispute.