Slaves in the North

Discussing with a relative the existence of slavery in the North.

I mentioned the idea/fact that New England settlers sometimes swapped Indian slaves (captured in war, particularly IIRC King Philips War) for black slaves by sending the former to British Caribbean colonies.   

On a  practical if very cynical basis, it makes sense.  Society recognized that when you won a war people were part of the booty.  Women to rape, men to work as slaves if they weren't killed.  (No conventions about treatment of prisoners of war back then.) But the problem with captures in the wars between the colonists and the Native Americans was it was relatively easy for the captives to escape and return to their people.  White colonists often did this, so would Native Americans.  The practical answer was to ship your war captives away to someplace where they were foreigners, where society was foreign.

(I suspect some part of the dynamic accounting for the capture and sale of black slaves to the slave traders was similar.  Keep your captives with you as slaves and they escape; sell them to the European trader who could provide weapons, etc. and it was a win.  Not for the slave.)