As the Grand Duchy of Lithuania expanded into Slavic lands, title to the acquired principalities was given to the Grand Duke's offspring or to others of his relatives. For example, Mindaugas granted Black Ruthenia with its center in Navahrudak to his son Vaišvilkas; Gediminas (Grand Duke of Lithuania from 1316 to 1341, sent his brother Fiodor to Kiev. This system had major disadvantages: the principalities remained semi-independent with loose ties to the central government. Rulers of these principalities could operate as powerful rivals to the Grand Duke, a situation that led to frequent power-struggles.