Goehrke Carsten. Geographische Grundlagcn der russischen Geschichte // Jahrbiicher der osteuropaischen Geschichte. — 1970. — Vol. 18. — S. 161–204; Khazanov A. M. Nomads and the Outside World. — Cambridge: Cambridge University Press, 1984; Taaffe Robert N. The Geographic Setting // The Cambridge History of Early Inner Asia / Ed. by Denis Sinor. — Cambridge: Cambridge University Press, 1990. — P. 19–40; Christian David. Inner Eurasia as a Unit of World History//Journal of World History. — 1994, — Vol. 5. — P. 173–211.