Arid plains.
From these low, accessible plains of adequate rainfall, which at first encourage primitive nomadism but finally make it yield to sedentary life and to dense populations spreading their farms and cities farther and farther over the unresisting surface of the land, we turn to those boundless arid steppes and deserts which Nature has made forever the homes of restless, rootless peoples. Here quiescence is impossible, the Völkerwanderung is habitual, migration is permanent. The only change is this eternal restlessness. While the people move, progress stands still. Everywhere the sun-scorched grasslands and waterless waste have drawn the dead-line to the advance of indigenous civilization. They permit no accumulation of productive wealth beyond increasing flocks and herds, and limit even their growth by the food supply of scanty, scattered pasturage. The meager rainfall eliminates forests and therewith a barrier to migrations; it also restricts vegetation to grasses, sedges and those forms which can survive a prolonged summer drought and require a short period of growth.
Annual Rainfall Of The World.
Distribution and extent of arid plains.
The union of arid plains and steppe vegetation is based upon climate, and is therefore a widely distributed phenomenon. These plains, whether high or low, are found in their greatest extent in the dry trade-wind belts, as in the deserts and steppes of Arabia, Persia, Sudan, the Sahara, South Africa and Central Australia; and in vast continental interiors, where the winds arrive robbed of their moisture in passing intervening highlands, as in the grasslands of our western plains, the llanos and pampas of South America, and the steppes of Central Asia. But wherever they occur, whether in Argentina or Russian Turkestan or the higher plains of Mongolia and Tibet, they present the same general characteristics of land surface, climate, flora and fauna, and the same nomadic populations of pastoral or hunting tribes. In them the movement of peoples reaches its culminating point, permanent settlement its nil point. Here the hunting savage makes the widest sweep in pursuit of buffalo or antelope, and pauses least to till a field; here the pastoral nomad follows his systematic wandering in search of pasturage and his hardly less systematic campaigns of conquest. It is the vast area and wide distribution of these arid plains, combined with the mobility which they impose on native human life, that has lent them historical importance, and reproduced in all sections of the world that significant homologous relation of arid and well-watered districts.
Pastoral life.