ic population, at no time very numerous in
proportion to the area over which it was spread, but liable on occasions
to accumulate, owing to a combination of circumstances, in this or that
portion of the region occupied, and at such times causing trouble to its
neighbors. From about the close of the third century B.C. symptoms
of such an accumulation had begun to display themselves in the tract
immediately north of the Jaxartes, and the inhabitants of the countries
south of that river had suffered from a succession of raids and inroads,
which were not regarded as dangerous, but which gave constant annoyance.
Crossing the great desert of Kharesm by forced marches, some of the
hordes invaded the green valleys of Hyrcania and Parthia, and carried
desolation over those fair and flourishing districts. About the same
time other tribes entered the Bactrian territory and caused alarm to the
Greek kingdom recently established in that province. It appears that
the Parthian monarchs, unable to save their country from incursions,
consented to pay a sort of black-mail to their invaders, by allowing
them the use of their pasture grounds at certain fixed times--probably
during some months of each year. The Bactrian princes had to pay a
heavier penalty. Province after province of their kingdom was swallowed
up by the northern hordes, who gradually occupied Sogdiana, or the tract
between the lower Jaxartes and the lower Oxus, whence they proceeded to
make inroads into Bactria itself. The rich land on the Polytimetus, or
Ak Su, the river of Samarkand, and even the highlands between the upper
Jaxartes and upper Oxus, were permanently occupied by the invaders;
and if the Bactrians had not compensated themselves for their losses by
acquisitions of territory in Afghanistan and India, they would soon
have had no kingdom left. The hordes were always increasing in strength
through the influx of fresh immigrants, and in lieu of Bactria a power
now stood arrayed on the north-eastern frontier of the Parthians, which
was reasonably regarded with the most serious alarm and suspicion.

The origin of the state of things here described is to be sought,
according to the best authorities, in certain movements which took
place about B.C. 200, in a remote region of inner Asia. At that time a
Turanian people called the Yue-chi were expelled from their territory on
the west of Chen-si by the Hiong-nu, whom some identified with the Huns.
The Yue-chi separated i