While the churches eventually worked out their differences and came to an initial agreement, both Nicholas I of Russia and Napoleon III refused to back down. Nicholas issued an ultimatum that the Orthodox subjects of the Empire be placed under his protection. Britain attempted to mediate, and arranged a compromise that Nicholas agreed to. When the Ottomans demanded changes, Nicholas refused and prepared for war. Having obtained promises of support from France and Britain, the Ottomans officially declared war on Russia in October 1853.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What month did the Ottomans declare war on Russia?
October