The End of Slavery in the North
There were a number of reasons why slavery ended in the North, and not all of the reasons were because of human rights issues or any regard for people of color. In fact, many of the reasons were economic. In 1807, Great Britain (which controlled the international slave trade) banned the trade entirely. This meant that the importation of enslaved people from Africa became far more difficult and far more expensive.
At the same time, the number of enslaved people in the South far outnumbered the numbers in the North, primarily because of two reasons:
(1) The slaveowners of the South had created a rape industry in which enslaved women were forcibly impregnated; this led to an extraordinary increase in the population of enslaved people.
(2) The use of slavery in the North was never as extensive as it was in the South where huge tracts of land were turned into tobacco, sugar, and rice plantations, and huge numbers of people were needed to produce the crops. In the North, the economy was based primarily on small farmers, small industry, trade, and banking. In other words, it was an economy of merchants, small farms, finance, and small businesses where lifetime ownership of other human beings wasn’t economically viable.
Finally, as greater numbers of immigrants began arriving in the North to work in the mills and factories, the new system of industrial capitalism—which relied on the ability to create profits by controlling labor costs through low wages and the freedom to lay off workers when necessary—found the system of slavery to be less efficient, especially when workers would walk off the job if pushed too far.
Beginning in the late 1700s, European nations began outlawing slavery, both as an institution and as a trade, and as mentioned above, Great Britain outlawed the international slave trade in 1807. The U.S. Congress outlawed the importation of slaves in 1808, though it did not prohibit the domestic slave trade.
After that, the Northern states began finally phasing out slavery, in part the result of two centuries of organizing by abolitionists and other human rights activists; in part, because the cost of purchasing and owning enslaved people was too high; and, in part, because it no longer made economic sense in a system that relied on the ability to get rid of workers when it needed to.