Answer:
However, Nigeria's most diverse feature is its people. Hundreds of languages are spoken in the country, including Yoruba, Igbo, Fula, Hausa, Edo, Ibibio, Tiv, and English. The country has abundant natural resources, notably large deposits of petroleum and natural gas.
It would be mainly that "<span>D. More than one person wishes to control the same piece of land" that generally </span>has been the main cause of land grant disputes over time, since land is of course limited and very valuable.
People give up some liberty in exchange for some protection of their remaining rights.
It dried up.
North Africa used to be a fertile grassland, even swampy in some spots, 12,000 years ago. By 1000 BC (actually quite a while before) it had dried up into what is the the largest desert i the world: the Sahara.