Why was Northern Africa isolated from the rest of the continent

The Sahara becomes the almost impenetrable barrier which throughout recorded history has separated the Mediterranean coast and north Africa from the rest of the continent. Hope this help ever thought I'm not a history  I'm a math guy!

Explanation:

might be agreeing to participate ethically with other european nations in the slave trade

or notifying other european nations when taking possession   of african territories

in 1897, pershing became a tactical officer at west point, and that's where he was given the nickname "black jack." pershing's first name is "john," for which "jack" is a nickname, and he was a white man who commanded black troops. hence "black jack".