allied with the Ottoman Empire and were determined to prevent that from happening. The historian A. J. P. Taylor argued that the war had resulted not from aggression, but from the interacting fears of the major players: Weakening of the Ottoman Empire: 1820–1840s 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, and the commission of atrocities by Ottoman military forces (see Chios massacre) further undermined the empire. The disbandment of the centuries-old Janissary corps by the Sultan Mehmet 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. In 1830, Greece became independent after ten years of war and the Russo-Turkish War (1828–29). 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. France took the opportunity to occupy Algeria, which had been under Ottoman rule, in 1830. In 1831, Muhammad Ali of Egypt, the most powerful vassal of the Ottoman Empire, declared independence. Ottoman forces were defeated in a number of battles, which forced Mahmud II to seek Russian military aid. A Russian army of 10,000 landed on the shores of the Bosphorus in 1833 and helped prevent the Egyptians from capturing Constantinople. "The reasons for the Tsar's disquietude are not obscure. Not Turkey alone was threatened by the advance of Ibrahim. The rights secured to Russia by a succession of treaties were also directly jeopardized. The substitution of a virile Albanian dynasty at Constantinople in place of the effete Osmanlis was the last thing desired by the Power which wished, naturally enough, to command the gate into the Mediterranean". Russia was satisfied with the weak government in Constantinople (Istanbul). As a result, the Treaty of Unkiar Skelessi was signed and greatly benefited Russia. It provided for a military alliance between the Russian and the Ottoman Empires if one of them was attacked, and a secret additional