It's not even a white/black thing. White people has had white slaves (millions), black people has had black slaves (also millions).
The Atlantic slave trade is just example of slavery. It has existed in many civilizations:
“Evidence of slavery predates written records, and has existed in many cultures. [...] the practice of slavery [...] proliferated after the invention of agriculture during the Neolithic Revolution, about 11,000 years ago.
Slavery was known in civilizations as old as Sumer, as well as in almost every other ancient civilization, including ancient Egypt, ancient China, the Akkadian Empire, Assyria, Babylonia, ancient Iran, ancient Greece, ancient India, the Roman Empire, the Arab Islamic Caliphate and Sultanate, Nubia and the pre-Columbian civilizations of the Americas.”