Are you talking about the Greeks, Romans, Babaloynians, Egyptians, Meads, Persians, Vikings, Spanish, English, Americans etc
Excuse me. I was referring to the modern era, i.e. since the world was understood to be not flat, but that it also included North and South America since 1492, and that the world revolved as it made yearly rotations around the sun.
Your list from ancient history strikes me as somewhat selective in an age when the political discussion can include reparations for slavery in the U.S.
How many other countries had a civil war because of slavery in modern times?
You asked who the first slave dealers were. The abomination of slavery seems to have been endemic to almost all cultures at one point or another whether it was called serfdom or slavery.