Why Africa is in its present state, I don't know. Again you're conflating several arguments to support of your central premise that Black people are less intelligent.
You also keep wheeling out PC'ness,I would use the term common human decency.
Different population groups are exposed to very different environmental conditions, which is why average scores vary. For this reason IQ scores are rising faster in some populations than others (average IQs of Kenyan children were shown to have risen by 26.3 points in 14 years). Similarly, black American IQs are rising at a faster rate than those of white Americans, while Jewish Americans went from having below average IQs at the time of the First World War to having above average IQs now.
Its idiotic to compare the IQs of different populations. When you remove IQ scores from the tool box of the scientific racists, the rest of their case (your case) is demonstrably a pile of 5hite.