Outside the questionably sort-of-European Ottoman Empire, wholesale slavery was dying out in Europe before the Triangular trade (plenty of serfdom and indentured servitude, but not the property from birth slavery.) I'm not really sure it was racism in the modern sense that moved slavery in the Caribbean from aboriginal peoples to Africans. Everything I've read just describes this as being a practical matter in that whites couldn't physically handle the work in that heat and the Caribbean aboriginal tribes were too intractable. Africans on the other hand could stand the conditions and, once ruthlessly enslaved and subdued, were less likely to revolt than native Caribbeans. That made this incredibly lucrative trade possible, so hello African slavery. From this in the late 16th Century it seemed racism was not born, but became much more ingrained and exacerbated, so it's quite likely racism as we know it became part of the white psyche because Africans were effective slaves. Prior to this practical shift, what racism seemed to exist was of the physical caricature type (Shakespeare's "thick-lipped Moor" and all that) which, while certainly unacceptable today, was not the subhuman idea of blacks that came after. Romans for example mentioned race very little. They were Emperors from Africa, and St. Augustine was at least half Berber (and this was before the Islamic Arab invasion.) It's telling that even though he thought of himself as Berber and African, there really is no concrete proof of his skin tone, because it wasn't all that important to him and those around him even in Rome or Milan. All the evidence suggests while he would not have resembled a Masai in skin tone, he wasn't exactly an Aryan either. Nobody seems to have cared enough to mention it in hundreds of writings by, for and against him though.
Once American slavery took hold, it lasted longer than just about anywhere certainly in the developed world in great part because of the racism that deemed blacks inferior and animalistic. Apologists (and to be fair, serious historians) will often point out that there was white slavery of a sort in the Americas, but it was neither of the same kind, or duration, or extent, as black slavery, and hopefully nobody needs to be convinced that the centuries of black slavery in the US followed by Jim Crow followed by sub rosa white supremacy movements have deeply inculcated racism that persists today.
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