Robert Farley
points out that it's not as if there was no US military involvement in Africa before the creation of a new Africa Command, it's just that responsibility for Africa was divided up in a pretty nonsensical way between different theater commands. AFRICOM organizes things more sensibly, and sets up a situation where the military officers making decisions about Africa have some incentive to develop meaningful knowledge of the continent.
This article available online at:
http://www.theatlantic.com/politics/archive/2007/07/in-defense-of-africom/43665/