The most important feature that ties North Africa/Southwest Asia together is many of the people follow Islam. A large number are also the same ethnicity, Arab, although there are many other ethnic groups in the area. These things are true of both Northern Africa, but not Africa South of the Sahara, and Southwest Asia, but not other parts of Asia. That is why those sections of the continents are studied together. Other important features of the Mideast are the abundance of petroleum, the difficulty in having enough water, and a high level of conflict.
hope that's not a lot??