In my History class, we recently learned about a Triangular trade system. One part of the system included Europeans purchasing slaves in Africa. The people from Africa who became slaves were weaker tribes in Africa that were taken over by stronger tribes right? The stronger tribes then became middlemen by then selling the people of weaker tribes to Europeans for resources.
My question is: During this time period, why didn't Europe cut out the middlemen in this trade system? They had firearms at the time and could've created some sort of colony on on of the piers of Africa right?
Most of my knowledge comes from the lectures of Richard Reid, whose book is here. I'll use British trade as an example as it's what I know most about.
I think what you need to do is consider context. The slave trade was not started by the British state itself and colonialism was never started by states roaming around just looking for things to control/make money off, it was more complex than that. Britain gave tacit approval, but the first slave traders were merchants looking to make a nice sum out of both providing manufactured goods to Africans and slave labour to the Americas.
Colonial control and empire came much later, and even when it did come, it came at often quite dramatic cost to imperial powers. Britain never really turned a net profit from African colonies or imperial holdings, even when bleeding them dry during the world wars.
Whether Britain could have made more money when the slave trade was still operating, I'm not sure. But a big part of the triangular trade was selling guns to Africans; that would have had to stop and a source of profit would be cut off. Then Britons would have had to land and establish a presence on the continent. They were doing this at this point, but more as explorers than invaders. They came up against disease, the Tsetse fly making transport difficult (no horses), and Africans who weren't best pleased about their arrival.
Not to mention the geography of Africa's coast making it difficult to land boats, let alone establish ports, except in specific places. But if you want one big reason I'd say it's because Europeans didn't know Africa. It would take a lot of extra capital to take a small army to Africa with which you could extract the slaves, which would suffer from disease like I've said, then even if you establish a base you wouldn't know where to find more Africans and you'd have to fight them on home turf to get them to come with you. It would be risky and likely unprofitable. I don't know if any examples of this exist. I also imagine undercutting those middlemen - generally quite strong military mercenaries, often provided European firearms - would not go down too well.
Also as an FYI, many historians of Africa don't like using the term "tribe" so sub-saharan Africa before colonialism. At this point it was "villages" slaves were taken from by groups of "mercenaries" without tribal affiliation. Tribes came later, and were largely proscribed by colonialists to African societies they didn't really understand. But as with many things like this, the idea became something real and stories and historical myth developed around them.
EDIT: refining wording
"never"? http://www.metmuseum.org/toah/ht/?period%3D11%26region%3Dafa. The interior of Africa never came under European sovereignty during the height of the slave trade for a variety of reasons; anti-malarial drugs and other technological innovations that made life in the jungle easier were a large part of this, as was the claiming of more profitable colonies (namely, the East & West Indies.)