Events, however, were precipitated in such a way that, without waiting for the opening of hostilities, the Turkish general in command of the fortress of Belgrade turned his guns on the city; this provoked the intervention of the powers at Constantinople, and the entire civilian Turkish population had to quit the country (in accordance with the stipulations of 1830), only Turkish garrisons remaining in the fortresses of Šabac, Belgrade, Smederevo, and Kladovo, along the northern river frontier, still theoretically the boundary of the Sultan’s dominions. After this success Prince Michael continued his military preparations in order to obtain final possession of the fortresses when a suitable occasion should arise. This occurred in 1866, when Austria was engaged in the struggle with Prussia, and the policy of Great Britain became less Turcophil than it had hitherto been. On April 6, 1867, the four fortresses, which had been in Serbian possession from 1804 to 1813, but had since then been garrisoned by the Turks, were delivered over to Serbia and the last Turkish soldier left Serbian soil without a shot having been fired. Though Serbia after this was still a vassal state, being tributary to the Sultan, these further steps on the road to complete independence were a great triumph, especially for Prince Michael personally. But this very triumph actuated his political opponents amongst his own countrymen, amongst whom were undoubtedly adherents of the rival dynasty, to revenge, and blind to the interests of their people they foolishly and most brutally murdered this extremely capable and conscientious prince in the deer park near Topchider on June 10, 1868. The opponents of the Obrenović dynasty were, however, baulked in their plans, and a cousin of the late prince was elected to the vacant and difficult position. This ruler, known as Milan Obrenović IV, who was only fourteen years of age at the time of his accession (1868), was of a very different character from his predecessor. The first thing that happened during his minority was the substitution of the constitution of 1838 by another one which was meant to give the prince and the national assembly much more power, but which, eventually, made the ministers supreme.