Answer: Herding animals.
In the zones of the semi-arid climate, there are huge areas of savannahs and steppes. Annual rainfall varies from 250 to 760 mm. This moisture is enough for grassy vegetation, but not enough for full forests. Severe droughts in these areas are a fairly common phenomenon. In open level spaces with rare trees prevail strong winds. The necessary conditions of existence of grassy vegetation of this zone are grazing of large herd animals which liberate vegetative communities from the accumulated straw and destroy bushes. The bulk of the plant grass mass is concentrated underground. The powerful root system allows it to accumulate nutrients and moisture. Herding animals stimulate the regeneration of vegetation.
Europeans competed for power either through acquisition of colonies or building up its industries. When their industries were strong, they would strengthen their armies as well. If that was not enough they would form alliances with other countries to protect their interest.
The decisive battle of the war was fought at Yorktown! A is the correct answer!
