Arizona: The 20th-Century State Among the Three

Arizona — Admitted Feb 14, 1912 (48th).
California — Sept 9, 1850 (31st).
Vermont — Mar 4, 1791 (14th).

Only Arizona joined in the 1900s. Its path: territory (1863) → railroad boom → copper → statehood push blocked by "too wild" reputation → Progressive-era reforms finally tipped the Senate.