Europeans and Americans conquered many places in the African Land and tried to exploit a lot out of them. This is the reason why Africa is poor. They didn't want them to be free as there are a lot of minerals and crops in this continent.
If Africa was free, they will be dominant in the global economy.
AFAIK there is no territory in Africa still under colonial rule, many African countries gained independence some 50+ years ago and that's more than enough time for them to have developed their territories.
@Coyster - I would argue that it's not that simple. History teaches us that when a colonial power leaves, the country doesn't just revert seamlessly back to its pre-colonial state. They leave behind power vacuums, or a system of hatred where the colonialist's local allies are left defenceless (Rwanda after Belgium left being a prime example). Sometimes they only leave in name, with 'free' elections rigged (example:
https://www.indymedia.org.uk/en/2007/08/377883.html) or puppet rulers installed. Often the departure is rushed and botched - because the colonialists are ceding all control, they have no interest any more in helping to manage the transition. Look at the mess of the Indian partition as an example here.
Colonialism leaves deep scars, and yes, even 50 years may not be long enough. Much of the instability in the Middle-East today can be traced back to the arbitrary divisions created by the British and the French more than a century ago, in the Sykes-Picot agreement (
https://en.wikipedia.org/wiki/Sykes%E2%80%93Picot_Agreement).
The world is not a level playing-field, with equal opportunities for all. Africans start at a severe disadvantage, due in large part to historic injustices perpetrated by the West.