You got a point.. It took a Civil War with the worst casualties in our military history to get it right. But -- we never had the level of sickness, despair, poverty and insecurity OUTSIDE of that Civil war to thwart us..
And it's not really just "decades" for Africa. There were transitions to self-rule going on as PART of the "development plan".. Hard to have a democratic nation state in a nation that's floundering in Civil rights, economic security, education, tribal tensions, etc..
You CAN argue that the Cold war and outside political influences are STILL OCCURING there... AFTER the French, Britain, German, Spanish were long gone. By the current superpowers like china, russia, US, angling for influence and stoking wars between Marxism and Capitalism, democracy and cultural tribal rule.
And then you have the environmentalists who want them to have solar panels and organic farming and NO widespread industrial or transportation growth to save the planet.. AND are kinda fond of "population control" programs as well...
EVERYONE'S got an agenda for the African continent.. What they NEED is LEADERSHIP to stand up to all this nannying and actually DEVELOP their nations in a culturally appropriate way without the rest of world coercing into plans and structures that aren't comfortable....