This Arizona history timeline of events traces the region’s development from millennia of Indigenous civilization through Spanish colonialism, Mexican sovereignty, and territorial expansion, to statehood in the 20th century and beyond.
Ancient Peoples and European Contact
The land that is now Arizona has been inhabited for thousands of years. The Hohokam civilization flourished in central Arizona from roughly 1500 BCE until around 1500 CE, developing sophisticated irrigation systems to farm the desert valleys. Other Indigenous peoples, including the Navajo, Apache, Hopi, and Pima nations, established permanent settlements, trade networks, and distinctive cultural practices across the region. Spanish explorers arrived in the 1500s, followed by Jesuit missionaries in the 1600s who established a chain of missions and presidios (military forts) throughout what they called Pimería Alta. This colonial period lasted until Mexican independence from Spain in 1821, but the Spanish and then Mexican presence remained relatively light; vast territories remained under the control and governance of Indigenous nations.
War, Purchase, and Territorial Growth
The Mexican-American War (1846–1848) reshaped Arizona’s political boundaries. The Treaty of Guadalupe Hidalgo transferred the northern portions of the region to the United States, with the international boundary running roughly along the Gila River. Six years later, the Gadsden Purchase brought the remaining southern territories, including what became Arizona’s capital region, into American hands. With these acquisitions complete, Congress established the Arizona Territory in 1863 under President Abraham Lincoln. The territorial period saw increased settlement, mining booms (particularly silver), railroad expansion, and growing conflict with Apache nations resisting forced relocation.
Statehood and the Modern Era
By the early 20th century, Arizona’s population and economic development had grown sufficiently to warrant statehood. On February 14, 1912 (Valentine’s Day), Arizona was admitted to the Union as the 48th state, the last of the original 48 contiguous states to achieve statehood. The occasion reflected Arizona’s journey from a sparsely settled colonial frontier through rapid territorial development into a fully integrated American state. In the decades that followed, Arizona continued to grow: the construction of major dams such as the Roosevelt Dam (1911) and later Hoover and Glen Canyon dams provided water for agriculture and urban expansion. The 20th and 21st centuries saw Arizona transformed from a mining and agricultural economy into a modern hub of technology, tourism, and metropolitan development, with Phoenix becoming one of the largest cities in the United States.
Frequently Asked Questions
What does this Arizona history timeline cover?
This Arizona history timeline of events covers the region from pre-Columbian Indigenous civilizations through Spanish colonialism, Mexican sovereignty, the Mexican-American War and Gadsden Purchase, the territorial period, and Arizona's admission as the 48th state on February 14, 1912.
Who first inhabited Arizona?
Indigenous peoples have inhabited Arizona for thousands of years. The Hohokam civilization flourished for millennia until around 1500 CE, and the Navajo, Apache, Hopi, and Pima nations maintained established territories and governance systems throughout the region before and after European contact.
When did Arizona become a U.S. state?
Arizona became a state on February 14, 1912, when President William Howard Taft signed the statehood proclamation, making it the 48th and last of the original 48 contiguous states admitted to the Union.
How did the United States acquire Arizona?
The northern portions of Arizona were acquired through the Treaty of Guadalupe Hidalgo (1848) following the Mexican-American War. The southern portions were acquired through the Gadsden Purchase (1854), a negotiated purchase from Mexico of approximately 30,000 square miles.