Comments by "Piotr Misiuna" (@contemporiser) on "Italy calls for more equal relationship with migration producing states" video.

I think the core reason is that they never got a grip on corruption. Colonization didn't help, but I don't think it was a source of it, If African nations was honest and didn't enslave their own people beforehand, they would probably end up more like India or China. They still work against themselves even today.
1