Inner Eurasia includes the lands dominated by the former Soviet Union, as well as Mongolia and parts of Xinjiang. These make up the heartland of the Eurasian continent. Inner Eurasia is a coherent unit of world history, for its societies faced ecological and military problems different from those of the rest of Eurasia and responded by evolving distinctive lifeways. Five dominant lifeways are described here, which have shaped the history of the entire region from prehistory to the present. Inner Eurasia is losing its distinctive features in the contemporary era.What makes Inner Eurasia so distinctive? For one, the absence of major barriers to military expansion make it a natural unit of military and political history. Two of the three largest empires ever created, the Mongol empire and the Russian empire, both emerged in Inner Eurasia. Furthermore, the region's low ecological and demographic productivity sharply distinguishes it from Outer Eurasia: Western and Southeast Europe, and Southwest, South, Southeast, and East Asia.
Christian outlines five dominant adaptations that have shaped the region's history: (1) hunting during the Paleolithic, (2) the rise of relatively sedentary but increasingly militarized pastoralism during the Neolithic, followed by (3) the emergence of pastoral nomadism and pastoral nomadic states like that of the Mongols, (4) the growth of agrarian autocracies like those of Kievan Rus and Muscovy, and (5) the Soviet command economy.
By the end of the twentieth century, however, Inner Eurasia may have lost its distinctiveness. Changes in industrial techology have begun to erase its ecological disadvantages, as abundant mineral and energy supplies compensate for low agricultural productivity. And changes in military technology have rendered much of the world into the equivalent of the single, vast plain that used to distinguish Inner Asia.
SOURCE: David Christian, "Inner Eurasia as a Unit in World History," Journal of World History 5:173-211.
UPDATE: In the comments, Randy McDonald notes his review of The Siberian Curse on his LiveJournal blog. It suggests that environmental conditions in Inner Eurasia--at least in the more inhospitable areas--might marginalize the area in a global economy where capital is attracted to more easily exploitable areas. There certainly seems to have been a net population outflow from the less hospitable reaches of Inner Eurasia now that the gulag and deportations aren't supporting an artificial economy there.