[joe_the_user]

The chart they show is clearly ridiculous - it's a blob, not a line at all. Moreover, it's easy to imagine high income creates stability rather than the opposite.

The thing is, most of Africa has been by default poor and dysfunctional for quite a while. A big factor is that a lot of Africans have been subsistence farmers for a long time [1]. A substance might actually be comfortable in some circumstances but they are outside the money since they produce the food and materials they need for survival (so they can live on "pennies a day"). However, the tendency in many third world nations has been that the arrival of Western medicine allowed substance farmers to have the ten-child families they imagine will make them rich and the result is acute poverty. Moreover, when most people are substance farmers, the elites/state/etc tend to gain their wealth through rent-seeking, squeezing the majority, rather than enterprise.

Development, which is honestly capitalist development, requires workers willing to leave their family farms and work for wages on things the world market needs. Elites have to be willing and able to profit from people leaving traditional agriculture rather than profiting from traditional agriculture. By this, the Rwandan genocide (sadly) was a logical event setting the stage for development (especially since a minority of the educated elites came, exacted some revenge and set to work ruling the country). The Black Death and the Enclosures were both important development

[1] Now, it should be note that so much Africa was subsistence farming by the 19th because the earlier slave/gun trade allowed the "Slave States" within Africa to wipe out many more organized/less cleptocratic societies.