The Crimean War (1853-56) was fought between Russia on the one hand and an alliance of Great Britain, France, Sardinia, and the Ottoman Empire on the other.
In 1851, Napoleon III seized power in France and used France's power to compel the Ottoman Empire to recognize France as the sovereign authority over the holy land. Russia denounced this claim, having previously been identified as the protector of Eastern Orthodox Christians in the Ottoman Empire. France forced the issue by deploying the fleet to the Black Sea; Russia responded with its own show of force.
In 1851, Russia sent troops into Moldavia and Wallachia. Britain, now fearing for the security of the Ottoman Empire, sent a fleet to join with the French.
Diplomatic efforts failed. The Sultan declared war against Russia in October of 1851. Following an Ottoman naval disaster in November, Britain and France declared war against Russia.
Most of the battles took place around the Black Sea, although there were some battles in Asia and the Pacific.
This war also saw the involvement of Florence Nightingale.