Spykman N. J. Geography and Foreign Policy // The American Political Science Review,1938. Vol. 32. № 1. P. 30.
Halperin, Charles. Russia and the Golden Horde: The Mongol Impact on Medieval Russian History. Indiana University Press, 1985.
Spykman N. J. Geography and Foreign Policy // The American Political Science Review,1938. Vol. 32. № 1. P. 30.
Halperin, Charles. Russia and the Golden Horde: The Mongol Impact on Medieval Russian History. Indiana University Press, 1985.