Slavery in the English Colonies of North America.

The first Africans in the English Colonies of North America were brought to Jamestown, Virginia in 1619. While laws and circumstances varied between colonies, essentially the enslavement of African Americans became legal during the development of each of the Thirteen Original English Colonies in North America.

Slavery became more prevalent in the southern Colonies due to warmer climatic conditions which were better suited to large scale plantation style agricultural. This was one of the reasons that slavery became more economically entrenched in the southern Colonies. Other factors such as soil fertility and immigration also influenced the demographics of slavery throughout the Colonies.

A small persistent group of anti-slavery Europeans had protested against the enslavement of Africans from the beginning in 1444. As the enslavement of Africans in the English Colonies of North America increased, anti-slavery sentiments in England steadely grew in numbers and in influence. By 1750 anti-slavery sentiment had become: The Anti-Slavery Movement.  The Anti-Slavery Movement began to influence British government policy concerning slavery.

By the time of the American Revolution started in 1776, a debate to abolish slavery had already begun in the English Colonies. This debate was serious in the northern Colonies and in 1777 New Hampshire, as a new state in the United States, abolished slavery. The new states of Maine, Massachusetts Pennsylvania and abolished slavery. In 1784, Connecticut, Rhone Island and Vermont abolished slavery in their states.

This was the start of a boundary between states where slavery was legal and states where slavery was illegal. This was particularly evident between Pennsylvania where slavery had been abolished in 1780, and the states of Maryland and Virginia which bordered Pennsylvania. Slaves from Maryland and Virginia began to cross into Pennsylvania seeking freedom there. Some Quakers in Pennsylvania supported claims of freedom made by Maryland and Virginia slaves when their owners attempted to recover their lost slave property.

In 1783 the United States and Britain signed the Treaty of Paris ending the Revolutionary War. In 1787 the United States Congress enacted the Ordinance of 1787, which was the final version of legislation enabling American settlement of lands acquired from Britain in the Treaty of Paris. This land was north and west of the Ohio River and so was named the Northwest Territory.

The completion of a survey, known as the Mason-Dixon Line, had been completed in 1767 to settle a boundary dispute between Pennsylvania and Maryland. Not sure exactly why, but around 1784 the Mason-Dixon Line was extended between Pennsylvania and Virginia all the way to the Ohio River. The Ordinance of 1787 created a slave free boundary zone in the Northwest Territory between the slave states of Virginia and Kentucky that reached all the way to the Mississippi River in the west. In the Missouri Compromise in 1820, the United States Congress formalized the use of Mason-Dixon Line as the name for the boundary between states where slavery was legal and state where slavery was illegal.

The reason for the original survey of the Mason-Dixon Line was to settle a border dispute between Pennsylvania and Maryland during the Colonial Period, and had nothing to do with slavery. Simply because of approximation and circumstance, the border between free states and slave states of the United States acquired the name Mason-Dixon Line. The border between Iowa and Missouri was added in 1846 and this more or less defines the extent of the Mason-Dixon Line.