The Northwest Ordinance passed on July 13th 1787 by act of the United States Congress of the Confederation.
The Northwest Ordinance [also known as the Freedom Ordinance, or the Ordinance for the Government of the Territory of the US North West of the Ohio River], passed unanimously on July 13th 1787. The ordinance created the Northwest Territory out the area south of the Great Lakes, north and west of the Ohio River and east of the Mississippi River. This piece of legislation set the precedent of westward expansion in the United States. The Ordinance called for the eventual creation of not less than three, or more than five new states. The act also banned slavery in the new territory, which in effect established the Ohio River as the line between slave and free states.
Other information about the Ordinance
Text of The Northwest Ordinance