Few historical events can illustrate the unpredictability of the future as vividly as the sudden rise of Genghis Khan's Mongol empire in the second and third decades of the thirteenth century. The energy and genius of the relatively small number of people who were at the core of this enterprise have baffled all historians trying to explain the phenomenon, just as the effects, ranging from horrifying massacres and devastations to periods of admirable cross-cultural exchange and stimulation, have never ceased repelling and attracting them.

The effects of the Mongol invasion and rule were complex and, as we have implied, of varying type and degree across the vast swath of Eurasia they covered. Three areas and civilizations, however, can be singled out as having been affected far more radically than the rest: China, Central Asia, and Russia. In all three, history can be broken down into two periods, pre-Mongol and post-Mongol.

The first enigma of the Mongol phenomenon is the relative insignificance of the tribes and territories where Genghis Khan had arisen. We have dwelt on Mongolia during its “Turkic” period, the sixth through tenth centuries; a contemporary observer could with some legitimacy have characterized Mongolia as the real and original Turkestan, land of the Turks, whether Kök Turks, Uighurs, Kyrgyz, or an amorphous conglomerate of contending tribes. Once the Kyrgyz had lost interest in Mongolia and withdrawn to their homeland in southern Siberia, and the Khitan lost theirs thanks to their transformation into a Chinese dynasty – both of which developments took place in the tenth century – Mongolia became a country of nomads, mainly Turkic, grouped into tribes but lacking any larger political cohesion or cultural dynamism.