In Federalist 54 by James Madison or Alexander Hamilton (or both) explained that the 3/5th provision incentivized the abolition of slavery. The Southern States could have the full representation which they wanted only by ending slavery: “if the laws were to restore the rights which have been taken away, the negroes could no longer be refused an equal share of representation with the other inhabitants.”
The Convention’s other slavery issue was the slave trade and setting a date for its termination. Again while many delegates were deeply opposed to the trade, those of the slave-states were adamant. Charles Pinckney put it simply, “South Carolina can never receive the plan if it prohibits the slave trade.” There had been a general agreement to set the end date as 1800. Then the Convention accepted a proposal by Charles Cotesworth Pinckney of South Carolina to extend the period until 1808. James Madison was devastated. “Twenty years will produce all the mischief that can be apprehended from the liberty to import slaves.”
Everybody wants to run for the tall grass and hide on this issue. It’s unnecessary, but progressives have used the schools for decades to train us to be deathly afraid of the slavery issue.
This did not just arise in the last 7 years. This is a half-century’s worth of work we are looking at.
One of the best explanations of all this from a Constitutional perspective that you’ll read/hear on this very thing comes from Frederick Douglass.
“The American Constitution and the Slave - Is the Constitution pro-slavery or anti-slavery?”
https://rumble.com/vrtwjm-the-american-constitution-and-the-slave-is-the-constitution-pro-slavery-or-.html
An Historical Research Respecting the Opinions of the Founders of the Republic, on Negroes as Slaves, as Citizens, and as Soldiers
Soils in the Chesapeake region were becoming less productive. Wheat was becoming important in Maryland and Virginia, which had previously relied more on tobacco. There was an expectation that slavery would eventually be abolished in those states. With more free states than slave states, it was hoped, the states further South might also rethink slavery and abolition.
The problem was that South Carolina, Georgia and the new states of Alabama and Mississippi had very good soil and climate for growing cotton, and there was great demand internationally for cotton, so slavery didn’t go away. North-South rivalries became stronger as the country moved westward and also played a role. The revolutionary spirit that had inspired the first wave of emancipation didn’t last long either.