Human activities that contribute to desertification include the expansion and intensive use of agricultural lands, poor irrigation practices, deforestation, and overgrazing. These unsustainable land uses place enormous pressure on the land by altering its soil chemistry and hydrology.
The Songhai Empire controlled the production and supply of Salt. This was a very important commodity which was known as white gold at the time.
At its peak the Songhai Empire was the largest and richest Empire in Africa and one of the most powerful in all of the Muslim world.
The cities of Timbuktu and Djenné became importing trading centers and remained one of the most important cities in Africa until the empire's demise.
Apart from salt, the empire grew rich due to its control over vast supplies of Gold, slaves, kola nuts, leather, and dates.
Eventually, the huge riches of the Empire attracted attention from other leaders of the region. In the last 20 years, the kings of Songhai were in constant feud with multinational armies which took a political and economic toll on the Empire.
The best option from the list would be that "A. <span>The U.S. purchased the Florida Territory from Spain and seven states were admitted into the union, since this was one of the few times that the US purchased land instead of taking it through force. </span>
