Why did some people enslaved in Northern states with gradual abolition laws remain enslaved well into the mid-nineteenth century?

- Some Northern slaveholders illegally sold the people they had enslaved to other states where slavery remained in full effect.

- Northern slaveholders only needed to free those they were currently enslaving but were free to continue to import enslaved people from other states or abroad.

- Gradual abolition laws only applied to the offspring of enslaved people, not the people enslaved when the laws were passed.

- Gradual abolition laws were rarely enforced.