 Complete the following phrase:  The Akkerman Convention was a treaty signed on October 7, 1826, between the Russian and the Ottoman Empires in the Budjak citadel of Akkerman present-day Bilhorod-Dnistrovskyi, Ukraine. It imposed that the hospodars of Moldavia and Wallachia be elected by their respective Divans for seven-year terms, with the approval of both Powers. It also provided for the retreat of Ottoman forces from both Danubian Principalities after their prolonged stay following military actions in 1821 that were carried in response to the Filiki Etaireía in the Greek War of Independence, and Tudor Vladimirescus 