>>>Could we invade and conquer most African countries, loot the place and turn a profit?
Don’t forget Africa was being mined for the diamonds. The human trafficking and slave labor was still a huge issue (and profitable).
African diamonds are located in very small specific locations. One could certainly capture and hold those spots and extract the diamonds profitably. What one cannot do is conquer and rule vast areas of countryside profitably.
The only guy I’m aware of who ever did it was Leopold of Belgium in the Congo Free State, and he did it by methods the Nazis might have flinched at.
Conquest and rule of a vast, poor country is just not profitable, unless there is some resource there in great demand elsewhere.
Take a look at the historical maps of European conquest of Africa. Only peripheral areas were conquered up through the mid-1800s, long after the outlawing of the slave trade. In 1835 only 10% of the continent was controlled by Europe.
There was an excellent reason for this. Europeans who invaded Africa died of disease. In the 1750s the average lifespan of a slave trader onthe Guinea Coast was well under six months.
The "Scramble for Africa" didn't really get going till the 1880s and ended just before WWI.
Most of Africa was colonized for decades, not centuries.