“ Henceforth, whatever popular usage might be, the title tsar was treated officially as the equivalent of that of king. Thus the Russian emperor is tsar (king) of Poland and of several other parts of his dominions. Thus, too, the prince of Bulgaria, on assuming the royal style, took the title of tsar of Bulgaria.
The title “White Tsar,” applied to the Russian emperor and commonly quoted as though it had a poetic or mystic meaning, is a translation of a Mongol word meaning “independent” (cf. the feudal “blanch tenure,” i.e. a tenure free from all obligation of personal service) . ”