What landform acts as a natural barrier between North Africa and the rest of Africa?

My first thought: The Sahara Reason: It covers a large portion of Africa. It covers 10 countries, which happen to be in the north of Africa. These ten countries are: Tunisia, Niger, Libya, Algeria, Sudan, Mali, Mauritania, Egypt, Morocco and Chad, I believe. Hopefully this helped and good luck.P.S. Sahara means Desert in Arabic so when you say Sahara Desert you are saying Desert Desert. :)