Final answer:
Under the Northwest Ordinance of 1787, a 'territorial legislature' could be formed when a territory reached 5,000 adult free male citizens. This allowed elected representation and was a stepping stone towards statehood, which could be pursued when the population surpassed 60,000.
Step-by-step explanation:
Under the Northwest Ordinance of 1787, when the adult free male citizens of a territory reached 5,000, a territorial legislature could be formed. This was a significant step towards self-governance, as it allowed for the election of a legislature by the settlers themselves, though the governor continued to be appointed by Congress. Once the population exceeded 60,000, the territory could draft a constitution, ensuring the prohibition of slavery and protection of religious freedom, and then apply for statehood. This law was instrumental in the organization and expansion of the United States, specifically pertaining to the territories in the Old Northwest, which would become states such as Ohio, Indiana, Illinois, Michigan, Wisconsin, and parts of Minnesota.