What does Africa have to do with suburbanization? Suburbs really didn't come into their own until the 1960s and 70s due to the interstate highway system. Sure, they started springing up in post WW2 US with the housing boom, but not to the scale they are now.
Just look at the cities in decline such as Detroit. Miles and miles of suburbs with almost no one living in them. These are areas that will never be gentrified. That is the nice thing about urban areas. You can have gentrification, ie urban renewal. You can fix up or rebuild dilapidated buildings, and get fresh residents to fill them, which allows for urban renewal on a massive scale. With fresh residents comes more money, which allows for more businesses to open. The slums end up getting pushed out towards the city limits leaving the inner city a vibrant, bustling commercial center, much like how it was pre-interstates. You get commerce right next to residential areas, if not mixed in, which means people don't have to spend anywhere near the time travelling to go shopping or to get to work. This leads to more people using public transit, walking, or biking, which leads to lower traffic congestion and less smog, which is never a bad thing.
I'll be curious to see what happens to suburbs in the coming years. It seems like the general consensus in urban planning now, even in suburbs is to create vibrant city centers and have clustered multi-family residential areas. I am seeing tons of town-house and condo complexes being built within reasonable travel times of commercial areas, which also allows for public transit to become more cost-effective. I am also seeing more and more young people shying away from the McMansion, 4 car garage, swimming pool, sprawling suburbia lifestyle towards smaller domiciles, closer to city centers. Let's be honest, who actually likes commuting 30+ minutes each way? You are dealing with serious wear and tear on vehicles, steep fuel costs, and just so much lost time.