Answer:
1. Most northern states outlaw slavery.
After the colonists gained independence from the British, Northern states moved to abolish slavery and by 1804, most Northern states had done so.
2. Congress outlaws importation of African Slaves to the US.
In 1807, Congress passed a law that outlawed the importation of African enslaved people to any American port. It took effect on the first day of 1808.
3. Abolitionists grow in number.
More and more people began to see slavery as a moral wrong and so the Abolitionist movement kept growing.
4. The Underground Railroad begins.
With more people opposed to slavery, smuggling enslaved people out of the South became a possibility and so the Underground railroad began and it is estimated that tens of thousands were able to escape using this method.
