Answer:
Northwest Ordinance of 1787.
Explanation:
The Northwest Ordinance was an act passed on July 13, 1787. This law created the Northwest Territory, in the current Midwest region. In addition, this law established the principle by which all the territories annexed to the United States would be incorporated as new territories that, if they met the required population parameters, could apply to be new states of the nation, instead of joining any of the 13 original states of the country. In this way, this law guaranteed that new states were incorporated into the Union as the country began to expand.
