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 part of New York and was not admitted until New York consented); two large additions to Nevada, which became a state in 1864, were made in 1866 and 1867. However, there have been numerous minor adjustments to state boundaries over the years due to improved surveys, resolution of ambiguous or disputed boundary definitions, or minor mutually agreed boundary adjustments for administrative convenience or other purposes. One notable example is the case "New Jersey v. New York", in which New Jersey won roughly 90% of Ellis Island from New York in 1998. In addition to the original 13, six subsequent states