part from a knowledge of the Sahara and its
peoples. All the Sudanese states were formed by invaders from the
northern desert, Hamitic or Semitic. [See map page 487.] The Galla or
Wahuma herdsmen of East Africa founded and maintained the relatively
stable states of Uganda, Kittara, Karague, and Uzinza in the equatorial
district; the conquerors remained herders while they lorded it over the
agricultural aborigines.[1098] In prehistoric times when the various
peoples of the Aryan linguistic family were spreading over Europe and
southern Asia, the superiority of the shepherd races must have been
especially marked, because in that era only the unobstructed surface of
the steppes permitted the concentration of men on a vast scale for
migration and conquest. Everywhere else regions of broken relief and
dense forests harbored small, isolated peoples, to whom both the idea
and the technique of combined movement were foreign.

[Sidenote: Scope of nomad conquests.]

The rapidity and wide scope of such conquests is explained largely by
the fact that nomads try to displace only the ruling classes in the
subjugated territory, leaving the mass of the population practically
undisturbed. Thus they spread themselves thin over a wide area. How
lasting are the results of such conquests depends upon the degree of
social evolution attained by the herdsmen. Genghis Khan and Tamerlane,
after the manner of overlords, organized their conquered nations, but
left them under the control of local princes,[1099] while their tribute
gatherers annually swept the country like typical nomad marauders. The
Turks are still only encamped in Europe. They too make taxation
despoliation. And though their dominion has produced no assimilation
between victor and vanquished, it has given political consolidation to a
large area occupied by varied peoples. The Hyksos conquest of Egypt
found the Nile Valley divided into several petty principalities under a
nominal king. The nomad conquerors possessed political capacity and gave
to Egypt a strong, centralized government, which laid the basis for the
power and glory of the Eighteenth Dynasty. The Tartars in 1279 A.D. and
the Manchus in 1664 conquered China, extended its boundaries, governed
the country as a ruling class, and left the established order of things
undisturbed. The Saracen conquest of North Africa and Spain showed for a
time organization and a permanence due to the advanced cultural status
of the sedent