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Arizona (/ˌærɪˈzoʊnə/ (listen); Navajo: Hoozdo Hahoodzo Navajo pronunciation: [xòːztò xɑ̀xòːtsò]; O'odham: Alĭ ṣonak Uto-Aztecan pronunciation: [ˡaɺi ˡʂonak]) is a state in the southwestern region of the United States. It is also part of the Western and the Mountain states. It is the sixth largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona shares the Four Corners region with Utah, Colorado, and New Mexico; its other neighboring states are Nevada and California to the west and the Mexican states of Sonora and Baja California to the south and southwest.

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.