I am well aware of the Articles of Confederation, but you said the United States Constitution, which is a very different thing.
As the US Constitution was the more permanent National Charter and governed subsequently to it's adoption, that document determines the rule of law in the US, and that document implicitly makes slavery legal in the US.
Had the Northern Republicans gotten their way, the original 13th amendment would have made slavery permanent.
Just shows what horrible people they were.
“the original 13th amendment would have made slavery permanent.”
I disagree. “ No amendment shall be made to the Constitution which will authorize or give to Congress the power to abolish or interfere, within any State, with the domestic institutions thereof, including that of persons held to labor or service by the laws of said State.”
Nothing in the Amendment prevents a state from outlawing the institution of slavery. As you have stated many times over, slavery would have died out eventually due to economic changes in our society. The Amendment does not prevent that from happening. So slavery was not made “permanent”.