The Crimean War was fought primarily to prevent Russian expansion into the Balkans and eastern Mediterranean, and to keep the great port of Constantinople out of Russian hands. British interests in India were also threatened and it was not, in truth, a Crimean war as the Crimea was one of three major theatres, the others being the lower Danube and in Asia Minor to the foothills of the Caucasus mountains.
If the Ottoman empire maintained its integrity, Russian ambitions could be contained and Turkish authority was growing increasingly enfeebled by the middle of the nineteenth century. Russia claimed to be the champion of the Greek Orthodox citizens of the Turkish empire. The Turkish Sultan decided the controversy over possession of the keys to the Church of the Hoy Sepulchre in Bethlehem in favor of the Catholic monks in December 1852. The Tsar of Russia immediately responded by sending an ambassador to Constantinople to argue the orthodox case and to protect the Sultan's Christian subjects. When the ambassador, Menshikov, arrived in Constantinople, Turkish troops were in the process of suppressing a rebellion in Christian Montenegro. Menshikov added to his list of demands that Turkish troops withdraw from Montengero. The Sultan was inclined at first to surrender, but the British ambassador, Lord Stratford de Redcliffe, encouraged him to reject the Russian demands. Menshikov left believing the Turks would change their minds, the Russian government announcing that they would occupy the Danubian provinces of Moldavia and Wallachia unless they received satisfaction.
Britain and France now intervened and despatched ships on June 15th to the Dardanelles to sustain the Turks. In Vienna the Austrians hastily arranged a conference to attempt to avoid a war, but the Sultan rejected a draft compromise backed by Britain, France and Russia. On July 3, 1853, the Tsar, ordered his troops across the river Pruth into Moldavia and Wallachia. Russia had the right, by treaty, to enter these provinces to maintain order, so war need not have developed but the Turkish government was prepared and willing to resist the Russian challenge and declared war on October 5, 1853.
Britain and France entered the war after the massacre of Sinope on November 30, 1853, earlier in the month, British and French fleets had violated the 1841 Straits Convention by sailing through the Dardanelles to the Sea of Marmara. The British government insisted they had entered the straits at the request of the Turkish and within a few days a squadron of the Russian Black Sea Fleet attacked a Turkish squadron, commanded by Omar Pasha, at Sinope on the northern coast of Asia Minor.
Both sides claimed that the other had fired first, but the result was the annihilation of the seven Turkish frigates and two corvettes by superior Russian warships. Britain and France demanded the withdrawal of the Russian fleet and troops in a note to the Tsar on February 27, 1854, the note was ignored and on March 28th Britain and France declared war.