Colonialism left Africa in turmoil when it ended. I understand due to America setting up a constitution and system of government there was a much greater chance of stability than in African countries which are still often corrupt and tyrannical. I'm more interested in economic interests. Did separation from the British government mean that private British ventures and companies in America, which I assume in the colonies were the majority, were no longer considered British? How did the American economy come into being and sustain itself?
I learned a really good explanation for this in a political science class in university, and will try now to remember some of the details...
I think part of it had to do with the US (and other former colonies like Canada) not having recruited the indigenous population to support the new systems put in place, such as sugar cane plantations, and things like that. We kind of just shunted away and decimated the indigenous populations here rather than integrating them in any way into the system (pushing them out into the worst territories, creating reserves, mass death my smallpox, etc). This was done deviously with false agreements, lies, trickery, betrayal, violence, war, etc., and I don't want to make it seem like the indigenous populations here were passive and naive but that's another issue.
So if you look at the US, its culture and population increasingly became based only on the colonizers, with the original indigenous population being marginalized.
African countries have had revolutions sparked by the original enslaved/oppressed peoples, the colonizers get up and leave, and they're left with the mess of a country to run.
I hope someone can give you a better answer, there is a hell of a lot more to it than this.