At the Constitutional Convention, the Committee of Detail proposed that “new States shall be admitted on the same terms with the original States.” That proposal would have taken the policy behind the Northwest Ordinance of 1787 and made it a constitutional imperative. But Gouverneur Morris wanted the equality of admitted states to be struck because he feared the political power of the Western states would “overwhelm” the East. Over the objections of James Madison, his motion to strike out the requirement of equality won by a vote of seven to two. He then moved to make sure that no state could be formed out of a previous state without the consent of the previous state as well as the “general legislature” (i.e., Congress). In this case as well, he wanted the Eastern states that still had claims to Western lands (viz., Virginia and North Carolina) to have a veto over whether their western counties (which eventually became Kentucky and Tennessee) could become states. This motion passed by a vote of six to five. Like the question of the establishment of lower federal courts, the Convention effectively passed the issue of the status of newly admitted states over to the political process.

Once the new Constitution went into effect, however, Congress admitted Vermont and Kentucky on equal terms with the original thirteen states and thereafter formalized the condition in its acts of admission for subsequent states, declaring that the new state enters “on an equal footing with the original States in all respects whatever.” Thus Congress, exercising the discretion allowed it by the Framers, adopted a policy of equal status for newly admitted states.

A number of observers, however, including Gouverneur Morris, had contended that Congress could admit states only from territory that the United States possessed at the time of the Constitution’s formation. That position was echoed by New England Federalists upset with Thomas Jefferson over the purchase of Louisiana. There is no indication of any such limitation, however, in the text or in the view of most of the Framers. Further, time and the admission of new states have made that argument irrelevant. Exercising its discretion, Congress admitted new states from newly acquired territory and opted to give equal status to each.

The Supreme Court adopted the view of Congress regarding the “equal footing” of new states and made it a constitutional requirement. In doing so, the Court chose to impose the very constitutional rule that the Framers had rejected. Pollard’s Lessee v. Hagan (1845) (“There can be no distinction between those states which acquired their independence by force of arms and those which acquired it by the peaceful consent of older states. The Constitution says, the latter must be admitted into the union on an equal footing with the rest.”). By its terms, the Admissions Clause sets the exclusive method by which territories may become states. Thus, Puerto Rico has no right to elect members to the House of Representatives (nor may Congress by statute create such a right), for it is not legally a “state,” no matter what “functional equivalents” to a state Puerto Rico may possess. Igartúa v. United States (2010). Congress may, however, create new Indian enclaves within a state without needing the consent of the host state because such enclaves are not on “equal footing” with the state from which they were formed. Carcieri v. Kempthorne (2007). 

The “equal footing” doctrine remains constant to this day but has engendered problems in construing the legal effect of conditions that Congress has placed on the admission of a num number of states.

According to traditional historical practice, Congress passes an enabling act prescribing the process by which the people of a United States territory may draft and adopt a state constitution. Many enabling acts contain restrictions, such as the prohibition of bigamy in the Utah, Arizona, New Mexico, and Oklahoma acts. The applicant state then submits its proposed constitution to Congress, which either accepts it or requires changes. For example, in 1866, Congress refused the proposed Nebraska constitution because it limited suffrage to white males. Upon approval of the new state constitution, Congress may direct the president to issue a proclamation certifying the entry of the new state into the United States. A number of states, however, drafted constitutions for submission to Congress absent enabling acts and were subsequently admitted.

Texas is a special case: it was an independent republic and, under the Resolution of Annexation, has the option of creating up to four additional states out of its territory. Some commentators have wondered whether, under the Admissions Clause, Texas can constitutionally exercise that option unilaterally, or whether those would-be additional states would have to petition Congress independently as well.

Although Congress’s enabling act becomes a “fundamental law” of the state, its provisions must give way to the “equal footing” rights of other states once the new state becomes a member of the Union. In Pollard’s Lessee, the Supreme Court held that an enabling act could not divest Alabama of its sovereign ownership rights to land under internal navigable waters, and in Coyle v. Smith (1911), the Court invalidated a provision in Oklahoma’s enabling act that constrained where the state could place its capital. The rule the Court has fashioned is that Congress can regulate the state through the enabling act only insofar as Congress could do so under one of its enumerated powers. Thus, under its power to regulate territories, Congress could, in its enabling act, require Utah to deny the franchise to women in the election of delegates to the state’s constitutional convention (at a time when the U.S. Constitution did not guarantee women’s suffrage), but that restriction could not bind Utah once it had become a state. Anderson v. Tyree (1895). More typically, enforceable provisions in enabling acts have included exemption of federal property from state taxation, the method of regulating public lands, and the rules of commerce among the Indians.

Finally, despite the ambiguous second semicolon in the clause, new states may be formed out of an existing state provided all parties consent: the new state, the existing state, and Congress. In that way, Kentucky, Tennessee, Maine, West Virginia, and arguably Vermont came into the Union. It is doubtful, however, whether a state could reassign territory (in a swap with another state for example), or whether Congress could “de-annex” to another sovereign any territory that was part of a state without the consent of the affected state.