There are different forms of slavery. The US was unique in that it was a system of race based chattel slavery, and really, the idea of “race” was invented alongside it.

Slavery in west Africa would often mean that the person would end up being integrated into the tribe over a long period of time (varies immensely group by group, but still the general trend). In the Middle East, Muslims were not allowed to hold other Muslims as slaves, so sometimes conversion could be a ticket out (there’s some funny complexities there).

Slavery in the US was a uniquely barbarous institution. It was industrialized, it treated people as resources. Perhaps an especially brutal Roman latifunda could compare in an individual’s experience, but even then, a freeman in Roman society would still be about equivalent to most every one else.

Slavery didn’t stop in the US after it ended. Tons of masters chose not to tell their slaves that the Emancipation Proclamation had freed them until sometimes decades after the fact. After the Civil War, the KKK ran a campaign to terrorize Black communities. Communities also immediately passed things like vagrancy laws, which started the system of slavery as punishment for a crime that we still have today.

There have been forces in the US attempting to minimize slavery since before the ink was even dry on the peace treaty. Please do not join them.

US slavery wasn’t the same as slavery from other regions for that time period.

While other imperialist nations had slaves (although many had ended it at some point earlier than the US did by a significant amount of time), they still viewed said slaves as humans, even if in some cases still lesser. They also had slaves from different nations and empires (this is relevant to the “viewed as humans” part).

In the US however, slavery was limited to only those considered of the “black race”, and those people weren’t considered humans. It’s why the 1 drop rule existed too - basically, if you were any percent “black”, you were considered “black” because you were essentially now seen as not fully human, but a hybrid.

This dehumanization meant that US slaves were treated far worse than any other slaves for the time period (in non war-time). To the point that slave owners even forcibly bred slaves for specific characteristics as if they were cattle - something that was never done in history as far as I’m aware by violent force, the closest being that one king in Europe who enslaved tall people and made them part of an elite “giants” army, where they got special treatment but could only have tall wives as well. This breeding program the US had was even one of Hitler’s inspirations for his eugenics programs many years into the future.

This also meant that owners could kill slaves without repercussion in absolute - and that was a big distinction to other imperialist nations at the time as well. Yes, other empires would overwork and kill their slaves (the Spanish in the Caribbean especially), but they also couldn’t just start killing wantonly without some type of repercussions from their monarchy, as some authority always still belonged to the crown state.

That was not the case in the USA. Killing your slave would be seen no different as killing your pigs or chickens. They were property in the absolute.

Another difference to most slavery in history is that you couldn’t really escape slavery. In other empires or nations, you could escape by either literally escaping a province or because there was a year limit to how long you could be a slave. In some cases you could even buy your way out.

That also wasn’t the case in the USA for the longest time, with the only methods of escape being making it to Canada or Southern Mexico / Central America. And if you did make it to Canada, getting kidnapped back to the USA wasn’t unheard of.

But in all, the biggest effect was that slaves were 100% dehumanized in the US - something that was not the case anywhere else. US slavery wasn’t just awful, but arguably the worst institutionalized forms of slavery in human history, especially including it’s duration.

Now, as to why slavery is at the root of why there’s still effects to this day, consider that slaves went from legally not being considered humans, to suddenly being humans by law. Do you think the millions who didn’t see them as humans would change their views just as fast? Even after hundreds of years, there’s still some that don’t view them as humans, but many many more that think of them as lesser. Essentially, the mentality is of imperial Europeans 250+ years ago.

To downplay that, would be the equivalent of Germany deciding to downplay the Nazi regime.