[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 sedentary Arabs drawn into the movement by religious enthusiasm.  The environment of Spain tended to conserve the knowledge of agriculture, industry, architecture, and science which they brought in and which might have cemented Spaniard and Moor, had it not been for the intense religious antagonism existing between the two races.

The history of nomad conquerors shows that they become weakened by the enervating climate and the effeminating luxury of the moist and fertile lowlands.  They lose eventually their warlike spirit, like the Fellatah or Fulbe founders of the Sudanese states,[1100] and are either displaced from their insecure thrones by other conquerors sprung from the same nomad-breeding steppe, as the Aryan princes of India by the Mongol Emperor, and the Saracen invaders of Mesopotamia by the victorious Turkomans; or they are expelled in time by their conquered subjects, as the Tartars were from Russia, the Moors from Spain, and the Turks from the Danube Valley.

[Sidenote:  Centralization versus decentralization in nomadism.]