Slavery and its abolition in the United States provided the context for the rise of Jim Crow, which was a bunch of government and social forces that prevented blacks from experiencing the same economic or educational opportunities as white people did until it was formally abolished in the Civil Rights Movement of the 1960's.

As an example, housing policy encouraged homeownership with government policies that were effectively only available to white people. In Chicago, neighborhoods were segregated into white and black neighborhoods, and the segregation was enforced by contracts and covenants (if an owner in a white neighborhood tried to sell or lease to a black family, the neighbors could sue). At the same time, banks, insurers, and government lenders refused to deal with homes in black neighborhoods, so those owners couldn't get mortgages or insurance and therefore could never buy homes. The neighborhoods excluded from access to financial support therefore could not take part in the U.S.'s post-war investment and prosperity. This was made even worse by the fact that rent in black neighborhoods was actually more expensive than white neighborhoods, despite the horrible conditions, because of the artificially constrained supply.

Similarly, black Americans didn't have access to the same schools or the same jobs, so they didn't have the opportunity to build wealth through earning wages, either.

So between getting shut out of investment and getting shut out of wage earnings, black Americans were unable to participate as fully in wealth creation until fairly recently. And because they started as chattel property, and marriage/inheritance are important property law institutions for transferring wealth intergenerationally, American black poverty traces a lot of its roots to the starting conditions at emancipation.

In the early development of the United States there was a very common view of slavery. There were a handful of slaves around that generally did household things, and a fair mix of them were European Indentured Servants (temporary slaves).

But then the plantation system kicked in. The plantation system really didn't make all that much sense in the north where certain cash crops didn't grow nearly as well. It made a lot of sense when it came to things like sugar, cotton, indigo, and similar crops. So, a ton of slaves were imported into the Caribbean and American South. Those that ended it up the Caribbean generally ended up on sugar plantations and died at much higher rates, those that ended up in the American South generally wound up on Indigo or Cotton plantations which were hard work but less immediately fatal. This meant that the slave population in the United States grew while the slave population in the Caribbean and Latin America was beholden to the slave trade.

In the United States you saw two rival political economies begin to develop. In the Northern States the cities were the basic economic unit, they developed factories early and went deep into maritime trade. The elites of the north were generally industrialists and merchants. In the Southern States the plantation was the basic economic unit in an export-oriented economy. The elites were land-owning aristocrats, who modeled themselves on European nobility.

So you had an industrial economy in the north that depended upon some tariffs to protect developing industry from more developed English competition, a strong currency, and cultivating a large internal economy. You had an export economy in the south that benefitted from no barriers to trade (which was only possible when you got rid of your own), a weak currency, and positive relations with foreign industrial bases. The two sets of interests were not diametrically opposed but they certainly didn't mesh. So there were tons of practical policy fights triggered by having slavery in only some part of the country.

Then you have the two distinct kinds of elites. The southern gentry defined their power by being descended from greatness, as their center of power came from inheriting land that was worked by slaves. The northern plutocrats were defined less by inheriting wealth and more by status-generating pursuits that also generated fortunes, in those circles money was hugely legitimizing. Both sides would look at each other and see little justifying their rival's status as elite. This precipitated a ton of fights, including the famous incident were a South Carolina Senator broke a cane over the head of a Congressman from Massachusetts for "reasons of honor" on the floor of Congress. That year's graduating class from the University of Georgia bought the senator a bigger cane.

Then there's the hypocrisy of rhetoric. When you are coming out with statements like "All men are created equal" and also holding slaves that can never not be slaves and their children are also automatically slaves because they aren't created equal there's some kind of serious disconnect. The "particular institution" (particular meaning "strange" or "weird") in the South was seen as a dying thing for much of the early United States, as through much of the Western World the economics of slavery had changed to the point it was being outlawed. The more labor-saving machines are used the less need there is to forcibly extract labor from others via slavery, after all. So, it was assumed by many in the American South that slavery was on the way out, but they couldn't jump the gun as freeing slaves would have eliminated more household wealth in the South than was destroyed by the Great Depression. Willing going through a Great Depression was too tough of a sell to overcome, so people kept on punting the issue.

Only, it didn't go away. New inventions kept slavery competitive, as new machines eliminated the need for slaves in the house other new machines increased the value of slaves in the fields. So, instead of this thing that made the North and South very, very different places that didn't get along going away, it just festered and got worse until it ripped the country apart.

The Civil War wasn't fought because southerners were all "grr... black people". The Civil War was fought because the slave economy led by a landed gentry was increasingly incompatible with an industrial economy led by merchants and industrialists. The Civil War was really hard on the US. Between 2% and 2.5% of all Americans died. For perspective 700,000 Americans died in the Civil War whereas only 419,000 (0.32% of the population) died in World War II. The Civil War had a huge and lasting impact on America, and the Civil War happened because of slavery.

So, good guys win, right? Everyone is happily ever after, right?

Well, no really. There were attempts to remake the American South in the image of the American North, but these efforts failed badly. Attempts to ship all the former African Slaves back to wherever they came from also failed (but not without creating Liberia). So, what happened? The American South tried to split itself into two along racial lines. It didn't go so well, but no one could stop it, so it happened.

It wasn't until very recently that overt attempts to suppress the black population of the South stopped, and even now we're dealing with tons of baggage from both slavery and the ultimately self-defeating ways that the north attempted to impose a different political economy on the south and the south took it out on the former slaves.

So, now there's a huge mess. It's an elephant in the room. It can't be undone, and it really can't be ignored. There's also no easy solution. So, slavery and its legacy is literally the most divisive thing in American history, it's caused more death and destruction in the nation than just about anything else. And despite it all it clearly profoundly shapes how Americans see themselves and other Americans.