In 1853, Russia provoked the Ottoman Turks into declaring war and then sank some of the Turkish fleet in the Black Sea which provoked Britain and France.
Britain and France sent 60,000 men to Crimea to attack Sevastopol by land and sea. Russia had 1 million men at this point.
The Russians were defeated at Balaclava and Inkerman in 1854, Sevastopol fell in 1855 and the humiliating Treaty of Paris was signed in 1856.