The Crimean War was fought to keep the balance of power in Europe from shifting too much in Russia's favor. England and France feared that Russia would try to control the Straits of Bosporus as well as seize the opportunity to defeat the Turkish Empire once and for all. Czar Nicholas I in his mind, saw this war as a holy crusade against the Moslem Turks, and could not understand, or face the fact, that past allies like France and England would turn against him.
In 1853, with English support, the Turkish Sultan declared war on Russia. Russia had recently invaded Turkish Moldava. England and France soon joined in against Russia because the Czar had refused to evacuate the invaded territory. Nicholas tried to negotiate a treaty of alliance with the Austrian Empire, suggesting that the Balkans, presently under Turkish control, become a joint Russo-Austrian protectorate. The Austrian emperor refused.
The war was not going well for Russia. The better armed British fleet attacked Russian naval bases in the White Sea, The Baltic Sea, and the Kamchatka peninsula. Russian forces kept on losing. The only success they had, came in Asia Minor. The Allies then attacked the Crimean Peninsula in full force. The Allies attacked the Russian fleet, which they destroyed, and then began to land their troops at the Russian naval base of Sevestapol.
For a year, the Russians held out in their base at Sevestapol, but as another winter approached, the Russian decided they could not hold out any longer. The base then quickly fell to the allies, and from that point, both sides were eager for the war to end.
Czar Nicholas had recently died, and the new czar, Alexander II, quickly gave in to the Allies' demands. The war officially ended in 1856 with the Treaty of Paris. Under the treaty, the balance of power was restored. Russia gave up all the areas it had conquered in the Crimea.
With allies having turned into enemies, the balance of power was again restored in Europe. No holy crusade ever came about to defeat the hated Ottoman Empire as Nicholas I had wanted. His dreams were shattered and he could not face the humiliation of this war. He died six months before the war officially ended. Some rumors said that he had poisoned himself.