The Tanzimat reforms did not halt the rise of nationalism in the Danubian Principalities and the Principality of Serbia, which had been semi-independent for almost six decades. In 1875, the tributary principalities of Serbia and Montenegro, and the United Principalities of Wallachia and Moldavia, unilaterally declared their independence from the empire. Following the Russo-Turkish War (1877–1878), the empire granted independence to all three belligerent nations. Bulgaria also achieved virtual independence (as the Principality of Bulgaria); its volunteers had participated in the Russo-Turkish War on the side of the rebelling nations.