What was the main aim of the northwest ordinance of 1787?

The Northwest Ordinance (officially An Ordinance for the Government of the Territory of the United States, North-West of the River Ohio) was unanimously passed on July 13, 1787. The primary effect of the decree was the creation of the Northwest Territory as the first organized territory of the United States outside the southern Great Lakes, north and west of the Ohio River, and in the east of the Mississippi River. On August 1789, the United States Congress approved the decree with slight modifications to the constitution.