How would African history be different if slaves had never been brought to the New World?
Okay so here goes nothing.
The question was "How would African history be different if slaves had never been brought to the New World?"
So, i think the one who asked this question most likely have an idea that slavery on exists in America. However kind sir, the answer is:
Slavery on Africa still exists
Why? Because there are also other another of slavery that exists in Africa and it operates for a thousand years, The Arabian Slave Trade in Africa.
What is it? Well, Arabian Slave Trade in Africa is a form of slave trade that is operated by the Arabs in Africa. It exists in Africa for a thousand years since the 7th century until the 20th century, where it was declining due to European "Scramble for Africa" in the late 19th century which made the Europeans control most of Africa, rendering Arab slavery was on the verge of declining.
So, IMO if the more commonly-known Atlantic Slave Trade never happened at the first place, then it wouldn't make any difference in slavery, apart from the fact that in this alternate world, African slaves never even knew about The New World and their population there, if exists later on, was most likely sparse.
Slavery itself exists in Africa and has always existed. So what would primarily be different, is that American and European racism towards Africans may never have got started.