The Crimean War was a military conflict fought from October 1853 to February 1856 in which Russia lost to an alliance made up of the Ottoman Empire, the United Kingdom, Kingdom of Sardinia and France. The immediate cause of the war involved the rights of Christian minorities in the Holy Land, then a part of the Ottoman Empire. The French promoted the rights of Roman Catholics, while Russia promoted those of the Eastern Orthodox Church. Longer-term causes involved the decline of the Ottoman Empire and the unwillingness of Britain and France to allow Russia to gain territory and power at the Ottoman Empire's expense. The war stood out for its "notoriously incompetent international butchery".
While the churches worked out their differences with the Ottomans and came to an agreement, the French Emperor Napoleon III and the Russian Emperor Nicholas I refused to back down. Nicholas issued an ultimatum demanding that the Orthodox subjects of the Ottoman Empire be placed under his protection. Britain attempted to mediate and arranged a compromise that Nicholas agreed to. When the Ottomans demanded changes to the agreement, Nicholas recanted and prepared for war. Having obtained promises of support from France and Britain, the Ottomans declared war on Russia in October 1853.
In July 1853, Russian troops occupied the Danubian Principalities (now part of Romania, then under Ottoman suzerainty). In October 1853, the Ottomans responded by declaring war. Led by Omar Pasha, the Ottomans fought a strong defensive campaign and stopped the Russian advance at Silistra (in present-day Bulgaria). A separate action on the fort town of Kars in Western Armenia led to a siege, and a Turkish attempt to reinforce the garrison was destroyed by a Russian fleet at Sinop (November 1853). Fearing an Ottoman collapse, France and Britain rushed forces to Gallipoli. They then moved north to Varna in June 1854, arriving just in time for the Russians to abandon Silistra. Aside from a minor skirmish at Köstence (today Constanța), there was little for the Allies to do.
Frustrated by the wasted effort, and with demands for action from their citizens, 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 and marched their way to a point south of Sevastopol after winning the Battle of the Alma (20 September 1854). The Russians counterattacked on 25 October in what became the Battle of Balaclava and were repulsed, however the British Army forces were seriously depleted as a result. A second Russian counterattack, at Inkerman (November 1854), ended in stalemate. The front settled into a siege involving brutal conditions for troops on both sides. Smaller military actions took place in the Baltic (1854-1856; see Åland War), the Caucasus (1853-1855), the White Sea (July-August 1854), and the North Pacific (1854-1855).
Sevastopol fell after eleven months. Isolated and facing a bleak prospect of invasion from the west if the war continued, Russia sued for peace in March 1856. France and Britain welcomed this development, as the conflict was growing unpopular at home. 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 there gained a degree of official equality, and the Orthodox Church regained control of the Christian churches in dispute.
The Crimean War was one of the first conflicts in which the military used modern technologies such as explosive naval shells, railways, and telegraphs. The war was one of the first to be documented extensively in written reports and in photographs. As the legend of the "Charge of the Light Brigade" demonstrates, the war quickly became a symbol of logistical, medical, and tactical failures and mismanagement. The reaction in Britain led to a demand for professionalisation, most famously achieved by Florence Nightingale, who gained worldwide attention for pioneering modern nursing while treating the wounded.
The Crimean War marked a turning point for the Russian Empire. The war weakened the Imperial Russian Army, drained the treasury and undermined Russia's influence in Europe. Russia would take decades to recover. The humiliation forced Russia's educated elites to identify the Empire's problems and to recognize the need for fundamental reforms. They saw rapid modernization of the country as its sole way to recover the status of a European power. The war thus became a catalyst for reforms of Russia's social institutions, including the abolition of serfdom and overhauls in the justice system, in local self-government, in education, and in military service.