Admission to the Union

The Admission to the Union Clause of the United States Constitution, oftentimes called the New States Clause, and found at Article IV, Section 3, Clause 1, authorizes the Congress to admit new states into the United States beyond the thirteen already in existence at the time the Constitution went into effect.

The Constitution went into effect on June 21, 1788, after ratification by 9 of the 13 states, and the federal government began operations under it on March 4, 1789. Since then, 37 additional states have been admitted into the Union. Each new state has been admitted on an equal footing with those already in existence.

Of the 37 states admitted to the Union by Congress, all but six have been established from an existing U.S. organized incorporated territory. A state so created might encompass all or a portion of a territory. When the people of a territory or a region thereof would make their desire for statehood known to the federal government, in most cases Congress passed an enabling act authorizing the people of that territory or region to frame a proposed state constitution as a step towards admission to the Union. Although the use of an enabling act was a common historic practice, a number of territories drafted constitutions for submission to Congress without one, but were still admitted to the Union.

An enabling act would detail the mechanism by which the territory would be admitted as a state following ratification of their constitution and election of state officers. Although the use of such an act is a traditional historic practice, a number of territories have drafted constitutions for submission to Congress absent an enabling act and were subsequently admitted. The broad outline for this process was established by the Land Ordinance of 1784 and the 1787 Northwest Ordinance, both of which predate the present U.S. Constitution.

...
Wikipedia