Resource thing is not quite true, parts of sub-saharan Africa have valuable resources and parts don't. Resources play a larger factor in African economies because they have little else. For example, while South Africa has gold mines but this place appears to lack water.
Resources play a large role elsewhere too. Norway is stinking rich because it has oil (and is able to manage this well and distribute the riches among the population). Large parts of Europe try to be at least somewhat friendly with Russia because it has oil, etc. etc.
