The Serbian forces quickly assumed control of Šumadija, reducing dahija control to just Belgrade. The government in Istanbul instructed the pashas of the neighboring pashaliks not to assist the dahijas. The Serbs, at first technically fighting on the behalf of the Sultan against the janissaries, were encouraged and aided by a certain Ottoman official and the "sipahi" (cavalry corps). For their small numbers, the Serbs had great military successes, having taken Požarevac, Šabac and charged Smederevo and Belgrade, in quick succession.