Northwest Ordinance of 1787
This provided a specific means by which the territories could become states. First they were subject to a Congress-appointed governor, secretary, and 3 judges. Once the population reached 5,000, it could elect an assembly from which electees Congress would appoint a council. Then once the population reached 60,000, the territory could apply for statehood. This also required each new state to form a constitution with a bill of rights, and it banned slavery from the territories until a newly-formed state decided otherwise.