The Northwest Ordinance was adopted on July 13, 1787, by the Confederation Congress, the one-house legislature operating under the Articles of Confederation. The Northwest Ordinance chartered a government for the Northwest Territory, provided a method for admitting new states to the Union from the territory, and listed a bill of rights guaranteed in the territory.
The prohibition of slavery in the territory had the practical effect of establishing the Ohio River as the geographic divide between slave states and free states from the Appalachian Mountains to the Mississippi River, an extension of the Mason–Dixon line. It also helped set the stage for later federal political conflicts over slavery during the 19th century until the American Civil War.