American Anti-Slavery Society organized.
The Anti-Slavery Movement began in Europe during the 1770s and rapidly spread to the United States during the American Revolutionary War. After the Revolutionary War, the Mason-Dixon, which had been surveyed in 1667 to establish a boundary between the English colonies of Maryland and Pennsylvania, eventually became the boundary between the Northern (Free) States and the Southern (Slavery) States.
The Anti-Slavery Movement in the United States, also known as the Abolitionist Movement, was already in its infancy during the early 1780s, when the settlement of the Northwest Territory was being contemplated. It is impossible to separate the Anti-Slavery Movement from the Underground Railroad.
The Anti-Slavery Movement influenced the United States Constitution and the Northwest Territory in many subtle and not so subtle ways. It is important not to confuse the Anti-Slavery Movement with the American Anti-Slavery Society, which became formalized in 1831. Of course the Anti-Slavery Society was formed because of the Anti- Slavery Movement, but the Anti-Slavery Movement represents a world-wide sentiment.