It was unprecedented in that western Europeans eventually ended government-supported slavery world wide.
Justification for slavery certainly took on a huge racist component in the US. From what I see that was a result of the cognitive dissonance between the revolutionary idea that “all men are created equal” and a slave-dependent economy in the South. The only way to reconcile the two ideas was make Africans less than fully human.
Outside of America, there was little connection between race and slavery. For example, about 20 million out of a total population of at total population of 74 million were serfs in Russia at the time of the US Civil War. In India, there were 9 million slaves out of population of about 40 million around that time. Slavery was also widely practiced in China. In these countries, virtually none of the slaves came from Africa, and the vast majority were native to the countries where they were enslaved.