"There are key differences between those states and Africa. The US, Canada, and Australia were settled by immigrants. The native populations were overwhelmed and pushed aside." 
Rubbish. What "native populations" were pushed out of Singapore, India, and Hong Kong?!
You see, all of this "blame Colonialism" nonsense is counter-productive. You can point to nation after nation that has shrugged off colonialism and become successful, so simply being colonized isn't sufficient excuse for national failures centuries later.
Rubbish. What "native populations" were pushed out of Singapore, India, and Hong Kong?! Read my post. I said those colonies didn't have diverse populations. India did somewhat, which is why they're having trouble in Kashmir, but on the whole, they're still the same tribal grouping they've always been.
Colonialism did cause problems in some countries, and to pretend that it didn't is to have one's head in the sand.