NOTE
This is not an apology for the leaders of the Confederacy or the politicians who seceded from the union based on myths about racial superiority. They were stupid and evil. Fuck those guys.
This is an apology for the 53% of African-Americans who live in the former Confederate states, and as a result suffer from economic discrimination resulting in higher infant mortality, increased crime, lower life expectancy, fewer educational opportunities, etc.
The result of the Civil War was 160 years of economic punishment which fell disproportionately on the very people the war was morally justified by claiming to benefit.
BACKGROUND
Perhaps the worst outcome of the early US period was the two-party system; by forcing groups into alliances with strange bedfellows, it conflated political positions which were on entirely different spectra.
For example, the Southern Agrarians held an ideal of small farmers with access to regulated markets under largely local control; the central government was supposed to manage interstate commerce and national defense, and not much more. Their natural allies, however, were large plantation owners, who liked local control of markets because they were wealthy and could manipulate them, and disliked the notion of powerful central government which could (and did) exceed its authority in the pursuit of social progress (these were, naturally, social conservatives, while the Southern Agrarians were less so).
On the other side, you had Northern Industrial interests who saw potential for rapid growth, if they could establish a powerful central government to allow exploitation of farmers and plantations, lowering their material costs and giving them a market advantage in foreign trade... which also required a standing military to "convince" reluctant trade partners to cooperate. Their "allies" were the burgeoning white middle class and Western (Ohio, at the time) farmers, who were propagandized against cheap black labor being used to compete with them (by claiming that lower prices for Southern goods was because of slavery and not unfair tariffs), ultimately coalescing into the Free Soil movement, which wanted to ship all black people, free or slave, back to Africa.
Combined with the nature of the bicameral legislature - the House being dominated by the more populous North, especially as slaves contributed less to the population count - this turned into a balance of power issue in the Senate, with new states only being added in pairs; one free, one slave. This was never a stable situation, though, and by the 1840s, when it became clear that the Southwest was not good agricultural land and so slavery simply could not effectively expand there, along with the international community turning against the practice, everyone realized that slavery would not last much longer.
IT'S THE ECONOMY, STUPID!
This is where the lack of economic regulation came back to bite us, hard.
Every other nation on Earth freed slaves by compensating the owners for their value, i.e. "buying" their freedom; this was not an ideological position, but a practical one. Plantation owners used slaves as collateral for loans, and if they were freed without compensation, the market collapsed and the economy ground to a halt.
Worse, because they saw this coming, the banks set up a securities market for slaves, which naturally inflated their value. In 1860, the total slave market cap was $17 Trillion in today's money.
In short, the country couldn't pay that; that was greater than the total value of literally everything else in the country: Land, mines, buildings, roads, all the gold in every vault, purse, or pocket, everything.
Now, the South had been stubborn about this for decades, but there was one last-ditch attempt in the debate about the resolution of the election of 1860 (which no one won, outright, and so it went to the House): Jefferson Davis proposed freezing expansion of slavery and a path to abolition (which might have taken less than 5 years) by transferring debt slowly to the government and paying it off with bonds, in exchange for making John C. Breckenridge president (as the combined Democratic vote well exceeded Lincoln's), but the abolitionists rejected the idea of paying for slaves and the Deep South insisted on a pro-slavery platform.
CHOICES
The South was faced with a choice: Accept uncompensated abolition of slavery and allow Northern banks to foreclose on literally everything in the South - every plantation, every farm, every mine, every building - or secede from the union.
Note that, from the very beginning, while deprecated, even the staunchest proponents of central authority had accepted that there was no legal bar to secession. During the Consititutional Convention, a proposal was made to insert a provision allowing the US government to militarily intervene to prevent secession; Madison replied:
"A Union of the States containing such an ingredient seemed to provide for its own destruction. The use of force agst. a State, would look more like a declaration of war, than an execution of a punishment, and would probably be considered by the party attacked that its allegiance to the Federal Union was dissolved."
The proposed provision was unanimously rejected, and never mentioned again, although during discussion of the New Jersey Plan, he said:
"A breach of any one article, by any one party, leaves any other party at liberty to consider the whole convention as dissolved"
Remember that, prior to the 14th Amendment, the US government was strictly limited to the powers expressly granted in the Constitution, and nowhere does it say that it can forcibly prevent a state from seceding, while the Xth Amendment explicitly confers any power not granted to the federal government to the states or the people. That is to say, secession is a power, and if the federal government does not have it, either the states or the people themselves must.
Otherwise, the notions of "freedom" and "self-determination" are lies.
CONSEQUENCES
First, naturally, the slaves were freed.
Ha! No, they almost all wound up right back on the same plantations doing the same things for the same people, often under even worse conditions (slaves were at least well-fed; they were valuable property). Those that tried to leave were arrested on contrived charges and sentenced to labor... right back on the plantation. The North which had claimed such concern for their welfare instituted crushing economic punishments which disproportionately fell on those very "freed" slaves.
Now, their descendants' prospects were improved; 50 years later, there started to be neighborhoods of successful black families... which were usually burned down by racist white pricks who had been told to blame black people for their problems instead of the system which had screwed them over (notably more often in the North than the South!). Today, certainly, things have improved... but not as much as they should have.
Second, the fundamental nature of the relationship between government and the people was inverted.
The original Constitution granted the federal government a strictly limited set of powers, outside of which, states and people could do as they wished. If you wanted to live in a state with an official religion, you could do that; or you could move to a state which was officially secular. Some states effectively banned private ownership of firearms, while other enshrined that right (at least to white people) in their own Constitutions.
The 14th Amendment inverted that; it said that, no, the Constitution grants certain, limited rights, i.e. free speech, religion, etc, and if it is not specifically listed, then there is no protection from the federal government, whose powers are now virtually unlimited. "Free speech," for example, can and has been punished by the government; some religions are privileged while others are denigrated, by law; the experience of a white man walking down the street with a gun on his hip is radically different from that of a black man walking down the street with a gun on his hip.
RESULTS
All of that being said, the legal protections for black people have never been stronger; abuses are more often addressed than ignored; and while there is still plenty to object to, those objections are steadily making progress. Keep it up!
The other result is not so great:
Our government is entirely under the control of a small, wealthy elite whose fundamental interests and values diverge from those of the vast majority of the population, and the intended checks and balances have been effectively dismantled by a collaborative, Establishment group of politicians in both parties who have stacked the courts with fascists and foregone Congress' traditional role as the check on the Executive branch, precisely because it allows unpopular policies to be enacted while disclaiming responsibility.
As Madison noted, the intended check on that happening was supposed to be the threat of individual states declaring the Compact to be nullified and simply not participating in the federal system, anymore; it was the Hamiltonians who won control of the government, though, and they never intended to abide by anything they negotiated.