1853

May 31 

A Russian ultimatum was issued to the Ottomans demanding to protect all Orthodox Christians (approximately 12 million at the time) in the Empire, and a treaty of alliance with the Ottomans was finalized.

Russia invaded two Romanian principalities to support the ultimatum.

October 

*The Ottoman Empire declared war on Russia. 

The Crimean War, also known in Russian historiography as the Eastern War of 1853–1856 (October 1853 – February 1856), was a conflict in which Russia lost to an alliance of France, Britain, the Ottoman Empire, and Sardinia. The immediate cause involved the rights of Christian minorities in the Holy Land, which was controlled by the Ottoman Empire. The French promoted the rights of Catholics, while Russia promoted those of the Orthodox Christians. The 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 Ottoman expense. Russia lost the war and the Ottomans gained a twenty-year respite from Russian pressure. The Christians were granted a degree of official equality and the Orthodox gained control of the Christian churches in dispute.

The Ottoman Empire declared war on Russia in October 1853 and suffered a major defeat that gave Russia control of the Black Sea. The Russian threat to the Ottoman Empire required control of the Black Sea, and the key was the Russian naval base at Sevastopol, on the Crimean peninsula. The allies realized that if they captured Sevastopol, they would control the Black Sea and win the war. France and Britain entered in March 1854. During most of the fighting in the Black Sea, a large French army and a smaller British army fought to capture Sevastopol. Death from disease was very high on both sides. After Sevastopol fell, the neutrals started aligning with the allies. Isolated and facing a bleak prospect if the war continued, Russia made peace in March 1856. The original superficial religious issues had already been resolved. The main results of the war were that the Black Sea was neutralized—Russia would not have any warships there—and the two states of Wallachia and Moldavia became largely independent.

The war was largely fought in and near Crimea, with smaller campaigns in eastern Anatolia, Caucasus, the Baltic Sea, the Pacific Ocean and the White Sea. This war is also known as the "Eastern War" (Russian: Восточная война, Vostochnaya Voina).

The war had a permanent impact. Through nationalist movements incited by the war, the present-day states of Ukraine, Moldova, Bulgaria, Romania, Greece, Turkey, Azerbaijan, Armenia, Georgia, and regions such as Crimea and the Caucasus all changed in small or large ways due to this conflict.

The Crimean War was one of the first conflicts to use 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 photographs. As the legend of the "Charge of the Light Brigade" demonstrates, the war quickly became an iconic symbol of logistical, medical and tactical failures and mismanagement. The reaction in Britain was a demand for professionalization, most famously achieved by Florence Nightingale, who gained worldwide attention for pioneering modern nursing while treating the wounded.

December 23

A British ultimatum to the Russians was rejected.