This was the nature of the seventeenth century Atlantic economy. That it has been well hidden from our schoolbooks and our historical understanding is an understatement. It also explains the demographic decline of the Eastern Indian Tribes a lot better than the hand wave of disease. The run of an epidemic was always brief and pretty final. Yet healthy tribes operated in the East into the nineteenth century and their final expulsion.
They did not die out slowly. The dying took place often long before Europeans even showed up and what the colonists were dealing with were those who had survived the worst and were actually on equal terms in disease resistance. Recall that Europeans got decimated by smallpox all through this era. And warfare claims only young men, because the women are taken into slavery at worst.
And there is our answer. The slave trade sold the men at least into the Caribbean for hard labour. More likely the women served as slaves on the coast because they were less likely able to escape. Their offspring would be predominantly hybrid stock with the associated vigor and the ready ability to step outside their visible racial designation.
Was this deliberate? Of course it was. You only have to read the treatment practiced on the Indians in California long since institutionalized to understand that the preferred offspring of an enslaved people were a hybrid stock. It is just that it is not discussed or committed to paper in contemporary sources, and so we have been allowed to forget what really happened over and over again.
It is difficult to piece the history of tens of millions of human beings lost to history and touched on by a mere handful of observers, who at best saw often only a village or two. To imagine from that a civilization of millions is to interpret modern North America from a brief visit to a Newfoundland out port. Archeology is slowly showing us a bit of the true histories of the Americas and allowing us to accept that our contact interrupted the lives of tens of millions.