1) Being black myself I can verify most black people aren't planning some kind of revenge mission to enslave "whitey". If black people wanted to do that we would have done it already. We've had almost 150 years for vengeance. Most of us are just taxpayers far too busy trying to scrape together a living, just like everyone else.
2) I could have sworn Detroit's problems have to do with corporations shipping overseas so they can exploit cheap labor? Since when has anything been burnt down in Detroit? Zimbabwe's problems stem from, aside from having an incompetent dictator for a leader who won't step down, the county being in debt up to their eyeballs to the IMF and World Bank, as well as little investment in industrialized farming.
South Africa is doing quite well. They have a middle class boom right now, 5-7% annual Real GDP growth and a huge growth in foreign investment. In 2010 South Africa was listed as a "Newly Industrialized Country" along with Brazil. S. Africa still has a lot of work to do tackling their ongoing problems with economic inequality and high crime rates (which have decreased some in the past few years) and AIDS rates but similar things could be said about China (the inequality problem).
Black people are in control in South Africa and several counties and cities in the US have a majority-black leadership and the sky isn't falling in S. Africa or most majority-black counties. For example, Prince George's County, MD is mostly-black and it's actually a well-off middle class county. Atlanta is mostly black and it's one of the cities in the US with the most economic growth in the past 10 years. There's nothing magical about melanin or facial features that makes you good or bad at managing things.