In the last 500 years, too, without any doubt. There were 21 million white slaves in Russia, emancipated only in 1861. USA and Brazil had ~4,5+2 million black slaves, combined.
My friend, I'm sure you mean well, but there are more slaves today than any other time in history, and I can assure you; they are not of one race.
"Usually" is not the best word here, I agree. What I meant is that it's "often the case". There are multitude of examples from Middle Ages in Europe(and before that), and Vikings etc. Not only people from Africa were were victims of slave trade.