Arizona states of Sonora and Baja California. Arizona is the 48th state and last of the contiguous states to be admitted to the Union, achieving statehood on February 14, 1912, coinciding with Valentine's Day. Historically part of the territory of "Alta California" in New Spain, it became part of independent Mexico in 1821. After being defeated in the Mexican–American War, Mexico ceded much of this territory to the United States in 1848. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase. Southern Arizona is known for its desert climate, with very hot summers and mild winters.
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