Answer:
The Northwest Ordinance of 1787.
Step-by-step explanation:
The Northwest Ordinance, passed on July 13, 1787 by the Confederate Congress, was a law whose object was the creation of the Northwest Territory, in what we now know as the Midwest. This territory encompassed the region located south of the Great Lakes, between the Ohio and Mississippi rivers. This was the first territorial expansion of the United States, which set the precedent for the incorporation of future new states into the territory of the Union. In addition, it was the first territory in which slavery was prohibited, thus marking an abolitionist trend in the north of the nation.