Rhodesia, known initially as Zambesia, is a historical region in southern Africa whose formal boundaries evolved between the 1890s and 1980. Demarcated and named by the British South Africa Company (BSAC), which governed it until the 1920s, it thereafter saw administration by various authorities. It was bisected by a natural border, the Zambezi. The territory to the north of the Zambezi was officially designated Northern Rhodesia by the company, and has been Zambia since 1964; that to the south, which the company dubbed Southern Rhodesia, became Zimbabwe in 1980. Northern and Southern Rhodesia were sometimes informally called "the Rhodesias".