It seems odd to me that it is usually placed separately in discussions about genocides, even though many millions of Africans died directly as a result of the inhuman brutality of the practice, and even many more millions suffered agonizingly for generations and generations over the numerous centuries the trade flourished.
I had the thought that perhaps it’s cast differently because it lacks a central aggressor (it was executed by vast networks of countries and treaties as “commerce,” including African leaders themselves), but I have no real basis for that thought other than a hunch.
What’s the real story?
Here is an answer from u/soswser to the same question from another thread dealing with the Atlantic slave trade. Basically, genocide means, "The deliberate killing of a large group of people, especially those of a particular ethnic group or nation." As destructive as the Atlantic slave trade was (With many Africans certainly dying en route to the Americas, and the slave trade even having an often unspoken but devastating and long lasting effect on Africa itself), the goal was not to deliberately kill off anyone, let alone cause the extinction of an entire ethnic group or race. The suffering and casualties, while definitely disgusting, aren't equivalent to the repeated, unrelenting torture and mass execution that say, Jewish and other groups people suffered during the holocaust.