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 an equal footing with those already in existence. Of the 37 states admitted to the Union by Congress, all but six have been established within 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 toward admission to the Union. Although the use of an