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 States was governed by a unicameral Congress, the Congress of the Confederation, which operated under authority granted to it by the Articles of Confederation, the nation's first constitution. The 11th Article authorized Congress to admit new states to the Union provided nine states consented. Under the Articles, each state cast one vote on each proposed measure in Congress. During this period, the Confederation Congress enacted two ordinances governing the admission of new states into the Union. The first such ordinance was the Land Ordinance of 1784, enacted April 23, 1784. Thomas Jefferson was its principal author. The Ordinance called for