New Mexico Territory of New Mexico for a half-century until admitted to the Union in 1912 as the 47th state (followed just under six weeks later by the Arizona Territory/State of Arizona, which became the 48th state, finally filling out the coast-to-coast continental expanse of the United States). As the route to California, New Mexico Territory was disputed territory during the American Civil War. Settlers in the southern part of the Territory willingly joined the Confederate States in 1861 as the newly organized Confederate Territory of Arizona, with a representative delegate to the Confederate Congress in the capital of Richmond. This territory consisted
Admission to the Union Admission to the Union The Admission to the Union Clause of the United States Constitution, often called the New States Clause, found at Article IV, Section 3, , 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