Democracy, free speech, rule of law, the Enlightenment, less corruption, a proletarian work ethic, secularism, and more. The fact that you people think the only reason the West is doing well is because of acts from hundreds of years ago demonstrates such a superficial understanding of history it boggles the mind. Ethiopia and Liberia were never colonised, yet they perform just as well as all the other colonised African nations. This demonstrates that colonisation alone is clearly only one of many factors impacting prosperity in the region. As someone who grew up in Africa, allow me to explain how nations are run: corruption. In Nigeria, for example, where I have some experience, it's not even called "corruption." It's just how they do business and politics. "Gift giving" is just good manners. With such a set of values in place, you should not have any doubts about the reason for the lack of African prosperity.
I should remind you that all African nations have practised various forms of colonisation and slavery throughout history. Depending on the definition of the word, very few nations on Earth have not. Your Noble Savages trope is as tiresome as it is factually incorrect. At some point these nations will have to take responsibility for their current circumstances. Blaming other nations won't solve their problems, and we're going to close the doors soon.