Arizona Territory 1877. The capital was finally moved to Phoenix on February 4, 1889. The territory was admitted to the Union as the 48th state on February 14, 1912. Proclamation to the People of Arizona. Arizona Territory The Territory of Arizona (also known as Arizona Territory) was a territory of the United States that existed from February 24, 1863 until February 14, 1912, when the remaining extent of the territory was admitted to the Union as the state of Arizona. It was created from the western half of the New Mexico Territory during the American Civil War. Following the expansion of the
Admission to the Union which predate the present U.S. Constitution. The Admission to the Union Clause also forbids the creation of new states from parts of existing states without the consent of both the affected states and Congress. The primary intent of this caveat was to give Eastern states that still had western land claims (there were four at that time) a veto over whether their western counties could become states. This clause has served the same function since, each time a proposal to partition an existing state or states has arisen. Article IV, Section 3, Clause 1: Between 1781 and 1789 the United