This was the Northwest 
Order of 1787 - Created and unified the Northwest Territory, the first 
organized territory of the United States, encompassing the lands on the 
north side of the Ohio River, and east of the Mississippi River. This
 ordinance would create the precedent of dividing and organizing the 
lands to the West, and when the population of a territory reached 60,000
 inhabitants or more, they could ask that this territory become a state. Another important fact of this Ordinance was that slavery was prohibited in these new states that would be created. The
 Ohio River was established as the boundary between the zone of 
forbidden slavery and legal slavery, which prepared everything for the 
emergence of free states and slave states.