Sub-Saharan Africa is, geographically, the area of the continent of Africa that lies south of the Sahara desert. Politically, it consists of all African countries that are fully or partially located south of the Sahara (excluding Sudan, even though Sudan sits in the Eastern portion of the Sahara desert). It contrasts with North Africa, whose Arab states are part of the Arab world. Somalia, Djibouti, Comoros and Mauritania are geographically part of Sub-Saharan Africa, but are also Arab states and part of the Arab world.
The Sahel is the transitional zone between the Sahara and the tropical savanna (the Sudan region) and forest-savanna mosaic to the south.
Since probably 3500 B.C.E, the Saharan and Sub-Saharan regions of Africa have been separated by the extremely harsh climate of the sparsely populated Sahara, forming an effective barrier interrupted by only the Nile River in Sudan, though the Nile was blocked by the river's cataracts. The Sahara pump theory explains how flora and fauna (including Homo sapiens) left Africa to penetrate the Middle East and beyond. African pluvial periods are associated with a "wet Sahara" phase during which larger lakes and more rivers existed.
The use of the term has been criticized because it refers to the South only by cartography conventions and projects a connotation of inferiority; a vestige of colonialism, which some say, divided Africa into European terms of homogeneity.