Admission into the Union

Article IV also grants to Congress the authority to admit new states into the Union. Since the establishment of the United States in 1776, the number of states has expanded from the original 13 to 50. Each new state has been admitted on an equal footing with the existing states. Article IV also forbids the creation of new states from parts of existing states without the consent of both the affected states and Congress. This caveat was designed to give Eastern states that still had Western land claims (including Georgia, North Carolina, and Virginia), to have a veto over whether their western counties could become states, and has served this same function since, whenever a proposal to partition an existing state or states in order that a region within might either join another state or to create a new state has come before Congress.

Most of the states admitted to the Union after the original 13 were formed from an organized territory established and governed by Congress in accord with its plenary power under Article IV, Section 3, Clause 2. The outline for this process was established by the Northwest Ordinance (1787), which predates the ratification of the Constitution. In some cases, an entire territory has become a state; in others some part of a territory has.

When the people of a territory make their desire for statehood known to the federal government, Congress may pass an enabling act authorizing the people of that territory to organize a constitutional convention to write a state constitution as a step towards admission to the Union. Each act details the mechanism by which the territory will be admitted as a state following ratification of their constitution and election of state officers. Although the use of an enabling 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. Upon acceptance of that constitution, and upon meeting any additional Congressional stipulations, Congress has always admitted that territory as a state.

In addition to the original 13, six subsequent states were never an organized territory of the federal government, or part of one, before being admitted to the Union. Three were set off from an already existing state, two entered the Union after having been sovereign states, and one was established from unorganized territory:

• California, 1850, from land ceded to the United States by Mexico in 1848 under the terms of the Treaty of Guadalupe Hidalgo.
• Kentucky, 1792, from Virginia (District of Kentucky: Fayette, Jefferson, and Lincoln counties)
• Maine, 1820, from Massachusetts (District of Maine)
• Texas, 1845, previously the Republic of Texas
• Vermont, 1791, previously the Vermont Republic (also known as the New Hampshire Grants and claimed by New York)
• West Virginia, 1863, from Virginia (Trans-Allegheny region counties) during the Civil War

Congress is under no obligation to admit states, even in those areas whose population expresses a desire for statehood. Such has been the case numerous times during the nation's history. In one instance, Mormon pioneers in Salt Lake City sought to establish the state of Deseret in 1849. It existed for slightly over two years and was never approved by the United States Congress. In another, leaders of the Five Civilized Tribes (Cherokee, Chickasaw, Choctaw, Creek, and Seminole) in Indian Territory proposed to establish the state of Sequoyah in 1905, as a means to retain control of their lands. The proposed constitution ultimately failed in the U.S. Congress. Instead, the Indian Territory, along with Oklahoma Territory were both incorporated into the new state of Oklahoma in 1907. The first instance occurred while the nation still operated under the Articles of Confederation. The State of Franklin existed for several years, not long after the end of the American Revolution, but was never recognized by the Confederation Congress, which ultimately recognized North Carolina's claim of sovereignty over the area. The territory comprising Franklin later became part of the Southwest Territory, and ultimately of the state of Tennessee.

Additionally, the entry of several states into the Union was delayed due to distinctive complicating factors. Among them, Michigan Territory, which petitioned Congress for statehood in 1835, was not admitted to the Union until 1837, due to a boundary dispute with the adjoining state of Ohio. The Republic of Texas requested annexation to the United States in 1837, but fears about potential conflict with Mexico delayed the admission of Texas for nine years. Statehood for Kansas Territory was held up for several years (1854–61) due to a series of internal violent conflicts involving anti-slavery and pro-slavery factions. West Virginia's bid for statehood was also delayed over slavery, and was settled when it agreed to adopt a gradual abolition plan.