Is it ensure, insure, or assure?
A war fought in the middle of the nineteenth century between Russia on one side and Turkey, Britain, and France on the other. Russia was defeated, and the independence of Turkey was guaranteed.
Note: Florence Nightingale came to prominence through her nursing service during the Crimean War. The poem “The Charge of the Light Brigade,” by Alfred, Lord Tennyson, describes a battle in that war.