African slavery was not necessary because white men couldn’t or would not do the work, as Australia has proven.
Slavery was necessary to avoid too large an underclass which would provoke warfare with native Americans.
In the North, wage slavery was far more economical than chattel slavery. Persons would be employed, paid, and have to find their own amenities.
White and Black people were enslaved under the Apprenticeship program.
A person was sold to a Master for training and continued to work for him and be supported by him until such time he was deemed Master of the trade.
As late as 1860 there was a population of black permanent apprentices in New Jersey. New Jersey was not a slave state.
Andrew Johnson, who became President after the assassination of Abraham Lincoln, had been an apprentice, owned by another person until he ran away.
Andrew Johnson’s hatred of the Plantocracy of the South was not because he opposed slavery or the dissolution of the Union. He wanted them destroyed because he had suffered enslavement.
Hence, The United States, land of the free, was built on the exploitation of workers.