The enslavement of thousands is a stain on the United States. The ripple effects are still being felt to this day.
Slaves were bought and sold in the northern colonies, but, by about 1800 these areas, states now in the new United States, had by and large forbidden the importing and sale of slaves. (That does not mean there were none; the slaves already present were allowed to remain.)
However, that does not mean merchants in the north were guiltless. Merchants, such as Lydia’s father, engaged in a three cornered trade in which New England businessmen took African slaves to the United States and the West Indies for work on the plantations, especially the sugar plantations.
The by product of making sugar, molasses, was shipped to New England for distillation into rum. That rum was exported to Great Britain and brought to Africa. The rum, and the profits from selling the rum, was used to purchase more slaves.
This trade was called the benign sounding Triangle Trade.