There is a huge difference between being a free state and welcoming blacks into the state.
I know most about Indiana and Ohio, so I will talk about them as examples.
It is true that all states previously part of the North West Territory were established as free states. This meant that slavery could not exist in those states.
It did not mean that blacks were welcome. You see, the overwhelming belief in the United States was that it was destined to be a country of western European Christians. Free states were meant to be rid of Indian nations and of blacks. Period.
The South needed new land because crop rotation was usually not practiced, and the Deep South land was producing less. They also believed that all land of the United States was to be a land of western European Christians, but blacks were acceptable as slaves/servants. Indian nations were not acceptable.
In the north, more and more people had never seen a black person. They were easily persuaded by stereotypes of animal behavior and intelligence. Indiana set a head tax on blacks entering the state of $300 in gold. That’s three years wages for a white laborer. It was impossible for a free black.
Many immigrants came from political states that had slavery, which, in fact, was almost all of the world. Most of the immigrants entered through New England harbors.
Indiana and Ohio shared the Ohio River with slave states. Indiana was settled by an influx of Kentuckians, with only a relatively few immigrants coming through the Great Lakes. Ohio was also impacted from the south, but also from the east.
Indiana was not happy that blacks from Kentucky ravished the local and state coffers. Bad masters sent unwanted slaves across the Ohio River and dumped them: the old, the ill, the disabled. Indiana had to pick up the tab.
And then when Kentucky masters moved to the state, there was the cost of court cases. Although there were few, it still angered the state capital of Corydon, located in southern Indiana. Even when the black person won freedom, it was another black person, now free, in Indiana. Poor whites saw that as competition for their jobs because blacks were paid less for the same work.
