History of North America

The northwest ordinance is considered a historical milestone because it?

The correct answer is it prohibited slavery in new territories.

The Northwest Ordinance of 1787 was an important law that defined the establishment of new territories in the area currently consisting of the states of Ohio, Indiana, Illinois, Michigan, and Wisconsin. One of its more progressive aspects for the era was to ban slavery there: "There shall be neither slavery nor involuntary servitude in the said territory".