(^60) Chapter Two
(1346). The plague bacillus probably became epidemic among bur
rowing rodent populations of the steppe for the first time in the four
teenth century. The infection was presumably introduced into the new
environment by Mongol horsemen who brought it back from their
campaigns in Yunnan and Burma, where endemic plague already
existed among local populations of burrowing rodents. Once the
bacillus established itself on the steppe, nomad populations found
themselves systematically exposed to lethal infection of a kind that
had never been known there before. Radical depopulation and even
the complete abandonment of some of the best pasture land of Eurasia
was the result.
By degrees, folkways effectively insulating steppe dwellers from the
new infection may have arisen. This certainly occurred in the Manchu
rian portion of the steppe, for such practices were in force there in the
1920s, when the most recent serious outbreak of plague among
human populations took place in that part of the world. But this sort
of readjustment took time. For two centuries or more after 1346,
steppe populations appear to have been much reduced in number by
their exposure to a new and very lethal disease that Mongol expansion
across hitherto insuperable distances had brought in its train.^72
The resulting interruption of demographic movement out of the
steppe towards cultivated lands disrupted what had long been one of
the fundamental currents of human migration in the Old World. By
the time the steppe peoples began demographic recovery, a new fac
tor, also traceable back to the Mongol breakthrough of older geo
graphic barriers, came into play: the use of firearms that could counter
nomad archers on the battlefield. Effective small-arms were not gener
ally available to civilized armies until after about 1550; but as they
spread, nomad superiority in battle suffered its final erosion. Instead
of being able to encroach on agricultural ground, as nomads had been
able to do since about 800 B.C., peasants began to invade the cultiva
ble portions of the Eurasian grasslands, making fields where pasture
had previously prevailed. The eastward expansion of Russia and the
westward expansion of China under the Manchus between 1644 and
1911 registered this reversal of human settlement patterns politically.
It is ironic to think that the diffusion of gunpowder weaponry, which
led to the final eclipse of steppe military power in the mid-eighteenth
- Arguments and evidence for this reconstruction of events are presented in William
H. McNeill, Plagues and Peoples (New York, 1976), pp. 149–65, 190–96.