That is correct - in nations like South Africa, and Libya, and Algeria and so on. Most of those nations, rich in natural resources are doing just fine, more or less. Many of them are going through the same slow transition to a democracy that the US did. The US did not become a democracy in just 25 years - it took a over a hundred and fifty years as a colony first, and it was exploding with wealth.
But nations like Mali and Mauritania are incredibly poor, and others, like Sierra Leone and Chad, like many African nations are rich in minerals - but the agriculture SUCKS, and they have horrible droughts. Without better subsistence, they'll never profit from their minerals.
Government instability isn't just culture, it's economics too. When you're starving, you'll support anyone who will feed you.