There are many things, but I would say that one of the things that has been very challenging for African countries is having a colonial past. There are a number of implications presently that are a result of having been formerly colonized. It had a deep effect on their economy. For example, many of those countries, once they gained independence, ended up exporting raw material but were not in the business of production themselves, and they were not doing manufacturing, which was very limiting on their economy.
The other thing is that many African countries have governance models. It's actually relatively recent that a number of African countries have democracies, because they're post-independence. Post-independence, many of those democracies even began more as single-party types of democracies and then evolved to be multi-party democracies. They are trying to make development achievements in an uphill battle, when the past has not made that easy for them.
I would add that climate change has a disproportionate impact on sub-Saharan Africa, even though countries in sub-Saharan Africa are actually very minimal contributors to climate change.