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In 1820-1830’s the Ottoman Empire endured a number of strikes which challenged the existence of the country. The Greek Uprising (began in the spring of 1821) evidenced internal and military weakness of Ottoman Empire and caused severe atrocities by Ottoman military forces (see Chios massacre). The disbandment of the centuries-old Janissary corps by Sultan Mahmud II on 15 June 1826 (Auspicious Incident) was a good deed for the country in the longer term, but it has deprived the country from its army forces for the nearest future. In 1827 the allied Anglo-Franco-Russian fleet destroyed almost all the Ottoman naval forces during the Battle of Navarino. In 1830 Greece becomes an independent state after 10 years of independence war and the Russo-Turkish War of 1828–1829. According to the Treaty of Adrianople (1829) Russian and European commercial ships were authorized to freely pass through Black Sea straits, Serbia received autonomy, and Danubian Principalities (Moldavia and Walachia) became the territories under Russian protection.

In what year was the Janissary corp disbanded?
1826