southern africa: why is famine afflicting places of such natural wealth?

Southern Africa is a region of enormous natural wealth. So why are 13 million people facing starvation? Drought and floods are certainly to blame, but man-made calamities, such as the decision of the authorities in Malawi to sell off a strategic 167,000-tonne grain reserve and President Robert Mugabe's controversial land seizures in Zimbabwe, have played a big part.