The Russians sent a fleet to Sinop in northern Anatolia. In the Battle of Sinop on 30 November 1853 they destroyed a patrol squadron of Ottoman frigates and corvettes while they were anchored in port. Public opinion in the UK and France was outraged and demanded war. Sinop provided the United Kingdom and France with the casus belli ("cause for war") for declaring war against Russia. On 28 March 1854, after Russia ignored an Anglo-French ultimatum to withdraw from the Danubian Principalities, the UK and France formally declared war.
When did the Russia disregard the ultimatum to leave the Danubian Principalities?
28 March 1854