The Civil War in the 1860s cost the lives of hundreds of thousands of Americans. It was also devastating to the economy because of the monetary cost of that war, along with the corresponding devastating damage so done to its infrastructure. That said, after it was all said and done, slavery no longer existed in the United States. The Constitution was amended to provide true civil rights to those that were previously enslaved, though in actuality, even today, America still has the same favored race, and those that are not part of that favored race are subject to living in a construct which has been demonstrably unfair to so many of them, despite laws that are meant to provide equality, liberty, and justice for all.
Something, though, that many people do not know or pay much attention to is that both Mexico as well as Canada also had slavery, but whereas eradicating slavery took a very bitter and bloody civil war, in which some States of the Union seceded from such, none of this happened in either Canada or Mexico. Regarding Canada, the Slavery Abolition Act, which took a long, tortuous path to become law, came into effect on August 1, 1834, which eliminated slavery throughout the British Empire. As for Mexico, President Vicente Guerrero issued a decree abolishing slavery on September 16, 1829, a few years after Mexico was declared independent of Spain. In both of these cases, the law eliminating slavery was passed not only because it recognized the humanity of all human beings, but also because slavery was a clear and present affront to a fair and civil society, and thereby unacceptable to a civilized people and its government.
The United States, therefore, was an outlier, and even though both countries contiguous to the United States had ended slavery, America insisted upon not only maintaining its institution but was intent, from the Southern perspective, along with those that sympathize with their position, to see that slavery be extended into new territories and States, which clearly created a division between those that desired to see slaves emancipated or at least reduced in number as opposed to those that were absolutely determined to see slavery continue forevermore, as this was an integral part and parcel of their plantation economies, structured for profit, above all.
The bottom line is that those that were fixated on the necessity and need for slave labor were, for the most part, determined to keep that slave labor because they believed that their continual path to profit, power, and social status necessitated their exploitation of that labor for their personal benefit. In other words, it was the profit so produced from those enslaved that meant that those that benefited directly and indirectly from the slave system would not countenance any interference with that institution, and hence they were willing to fight for their "right" to enslave other human beings, which is to the lasting shame of the United States, which was unable to legislate slavery out of existence, but instead had to fight a Civil War, which ultimately ended that slavery but has yet to end the negative aftereffects of having enslaved so many for so long.