The Russo-Turkish War of 1828–1829 was sparked by the Greek War of Independence of 1821–1829. War broke out after the Ottoman Sultan Mahmud II closed the Dardanelles to Russian ships and revoked the 1826 Akkerman Convention in retaliation for Russian participation in October 1827 in the Battle of Navarino. The Russians laid prolonged sieges to three key Ottoman citadels in modern Bulgaria: Shumla, Varna, and Silistra. With the support of the Black Sea Fleet under Aleksey Greig, Varna was captured on 29 September. The siege of Shumla proved much more problematic, as the 40,000-strong Ottoman garrison outnumbered the Russian forces. Faced with several defeats, the Sultan decided to sue for peace. The Treaty of Adrianople signed on 14 September 1829 gave Russia most of the eastern shore of the Black Sea and the mouth of the Danube. Turkey recognized Russian sovereignty over parts of northwest present-day Armenia. Serbia achieved autonomy and Russia was allowed to occupy Moldavia and Wallachia.