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 President would issue a proclamation announcing that a new state has been added to the Union. While Congress, which has ultimate authority over the admission of new states, has usually followed this procedure, there have been occasions (due to unique case-specific circumstances) where it did not. Congress is under no obligation to admit states, even in those areas whose population expresses a desire for statehood. 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