The Crimean War was fought between the Russian Empire and an alliance of the Ottoman Empire, the Second French Empire, the United Kingdom of Great Britain and Ireland, and the Kingdom of Sardinia-Piedmont from October 1853 to February 1856. Geopolitical causes of the war included the Eastern question (the decline of the Ottoman Empire), expansion of Imperial Russia 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.

The war's proximate cause was Tsar Nicholas I's demand that the Ottoman Empire's Orthodox subjects be placed under his protection. After the Sublime Porte's refusal, Russian troops occupied the Danubian Principalities in July 1853. The Ottomans declared war on Russia in October. Fearing the growth of Russian influence and compelled by public outrage over the annihilation of the Ottoman squadron at Sinop, Britain and France joined the war on the Ottoman side in March 1854. The Russian advance was halted at Silistria in June.

In September 1854, after extended preparations, allied forces landed in Crimea in an attempt to capture Russia's main naval base in the Black Sea, Sevastopol. They scored an early victory at the Battle of the Alma. The Russians counterattacked in late October in what became the Battle of Balaclava and were repulsed, and a second counterattack at Inkerman ended in a Russian defeat. The front settled into the 11-month Siege of Sevastopol, involving brutal conditions for troops on both sides. Smaller military actions took place in the Caucasus (1853–1855), the White Sea (July–August 1854) and the North Pacific (1854–1855). The Kingdom of Sardinia-Piedmont entered on the allies' side in 1855.

Crimean War
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Sevastopol ultimately fell after a renewed French assault on the Malakoff redoubt in September 1855. Diplomatically isolated and facing the prospect of invasion from the west if the war continued, Russia sued for peace in March 1856. France and Britain welcomed the development due to the conflict's domestic unpopularity. The Treaty of Paris, signed on 30 March 1856, ended the war. It forbade Russia to base warships in the Black Sea. The Ottoman vassal states of Wallachia and Moldavia became largely independent. Christians in the Ottoman gained a degree of official equality, and the Orthodox Church regained control of the Christian churches in dispute.