In the early 1800s, the Ottoman Empire suffered a number of existential challenges. The Serbian Revolution in 1804 resulted in the autonomy of the first Balkan Christian nation under the empire. The Greek War of Independence, which began in early 1821, provided further evidence of the empire's internal and military weakness. The disbandment of the centuries-old Janissary corps by Sultan Mahmud II on 15 June 1826 (Auspicious Incident) helped the empire in the longer term but deprived it of its existing standing army in the short term. In 1827, the Anglo-Franco-Russian fleet destroyed almost all of the Ottoman naval forces at the Battle of Navarino. The Treaty of Adrianople (1829) granted Russian and Western European commercial ships free passage through the Black Sea straits. Also, Serbia received autonomy, and the Danubian Principalities (Moldavia and Wallachia) became territories under Russian protection.
Russia, as a member of the Holy Alliance, had operated as the "police of Europe" to maintain the balance of power that had been established in the Congress of Vienna in 1815. Russia had assisted Austria's efforts in suppressing the Hungarian Revolution of 1848, and expected a free hand in settling its problems with the Ottoman Empire, the "sick man of Europe". However, Britain could not tolerate Russian dominance of Ottoman affairs, which would challenge its domination of the eastern Mediterranean.
Britain's immediate fear was Russia's expansion at the expense of the Ottoman Empire. The British desired to preserve Ottoman integrity and were concerned that Russia might make advances toward British India or move toward Scandinavia or Western Europe. A distraction (in the form of the Ottoman Empire) on the British southwest flank would mitigate that threat. The Royal Navy also wanted to forestall the threat of a powerful Russian Navy. French Emperor Napoleon III's ambition to restore France's grandeur initiated the immediate chain of events that led to France and Britain declaring war on Russia on 27 and 28 March 1854, respectively.