It was correlated with ethnicity as you note, but it was not ethnically driven as it was in the Americas.
There were African Roman Emperors and African slaves and Germanic slaves and Germanic soldiery in the Empire.
Greek city states might be just as likely to enslave other Greeks as they would enslave non-Greeks.
In the world of the western 1700’s and early 1800’s, slavery was essentially race related. No?
Yes, I agree. As a result of the changing European economy in the Middle Ages, slavery largely died out in Europe (setting aside the problem of the persistence of serfdom in the Russian Empire and other far eastern lands).
Slavery came back when during the voyages of exploration the Portuguese invented the African slave trade. The huge numbers of African slaves transported to the New World lead to the association of slavery with race. And, of course, as slavery came under attack as immoral, its defenders attempted to justify it on racial grounds.
To the contrary, it was almost always ethnically-driven. In the ancient world (setting aside the Roman Empire, which, as I have said, was more advanced), typically, relatively homogenous ethnic groups made war on ethnically different neighboring peoples and made their captives of wars into slaves.
There were African Roman Emperors and African slaves and Germanic slaves and Germanic soldiery in the Empire.
I don't know why you are trying to take issue with me on the point of the Roman Empire, as I have already said the Roman Empire represented a major civilizational advance and a departure from typical practices in the ancient world.
Greek city states might be just as likely to enslave other Greeks as they would enslave non-Greeks.
In the case of the Greeks also, as I have said, they typically took as slaves captives of other Greek tribes defeated in war. The helots, for example, were from the tribe of the Messenians and were made to serve the Spartans after the Spartans defeated the Messenians in war.
In the world of the western 1700’s and early 1800’s, slavery was essentially race related. No?
The enslavement of the slaves used in the Western Hemisphere originated in largely the same way as slavery typically always had. One tribe or ethnic group (in this case black Africans) defeated another tribe or ethnic group (also black Africans) in war and made the captives into slaves. Only in this case, the enslavement happened in West Africa and the leaders of the victorious tribe sold their slaves to Portuguese, and later other European, slave traders to be transported and used as slaves in other lands.
The insistence on drawing a strong distinction between slavery between different races as opposed to slavery between different ethnicities is of little value. Killing and enslaving people who are ethnically different is little different from killing and enslaving people who are racially different, and one should not consider tribalism any better than racism, because in fact it differs little from it.