There were 100s of rum factories in New England...operating for one purpose..trade for slaves.
Yankee slave traders were a minor part of the slave trade. Out of 12 and a half million slaves taken from Africa to the New World, a little over 300,000 were on American ships link. And of course, relatively few slaves were ever sold in the north, compared to the south. Your own map shows that. So I don't think it's a far reach to say that more slaves died on southern plantations than ever died on Yankee slave ships.
Thanks for an extraordinarily interesting link.
It's worth summarizing:
So the argument that many Northerners ever got rich on the slave trade is just bogus.
Indeed, I'd suggest the opposite: the reason Southerners, especially Virginians, accepted Constitutional restriction on importing slaves was because a shortage of supply drove prices for existing slaves ever higher.
This benefited hugely the old plantation classes in states like Virginia.
“It followed that the large capital that had been accumulated in that trade, thus forcibly driven from commerce, betook itself to manufacturing, and the “free traders” of New England became clamorous for “protection.”
Since then the capital earned in commerce and in the slave-trade has enjoyed a monopoly of navigating, importing, and manufacturing for the South, getting large pay, swollen by protective duties, in the proceeds of slave-labor.
In the mean time, if the South had ceased to employ northern shipping for the importation of negroes, it began to furnish a much more extensive employment for it in the exportation of cotton.”
Southern Wealth And Northern Profits, As Exhibited In Statistical Facts ... By Thomas Prentice Kettell