Final answer:
Washington had to follow the steps set out in the Northwest Ordinance of 1787, reaching a sufficient population, and ensuring internal sovereignty and recognized boundaries to apply for statehood. A constitution forbidding slavery and ensuring religious freedom was mandatory.
Step-by-step explanation:
The process for a territory like Washington to attain statehood was primarily outlined in the Northwest Ordinance of 1787. Initially, a territory with fewer than 5,000 white adult males was governed by a governor and judges appointed by Congress. As the population increased, the territory could form an elected legislature when reaching between 5,000 and 60,000 white male inhabitants. Importantly, when the population exceeded 60,000, the territory could draft a constitution that forbade slavery, upheld religious freedom, and then apply for statehood. Congress had the authority to grant statehood, which also meant self-government was achieved. Additionally, the Northwest Ordinance barred slavery, with specific exceptions.
Beyond the guidelines of the Northwest Ordinance, there were general requirements related to available population, established borders, as well as internal sovereignty where the territory must have control over its domestic and foreign policies. Furthermore, a territory like Washington had to ensure that it met any additional constitutional provisions that touched on the admission of new states and matters like the prohibition of forming new states from existing states without consent.