It was a watershed event that shaped the history of a relative new republic. Congress outlawed slavery in the nation’s Northwest Territory on July 13, 1787. The territory was an expansive area of the United States that was south of the Great Lakes and north and west of the Ohio River. It is also east of the Mississippi River. The prohibition of slavery in the territory had the practical effect of establishing the Ohio River as the boundary between free and slave territory in the area between the Appalachian Mountains and the Mississippi River. The fact that the territory was an area where slavery was outlawed caused an intensification of a national debate on slavery. It also fueled a national competition over the states that would be admitted into the union and whether they would be added as free or slave states. It was a controversy that would ultimately lead to the nation’s Civil War.

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