Which state was the last to join the United States?

Hawaii is recognized as the last state to join the United States, achieving statehood on August 21, 1959. This significant event marked the conclusion of the territorial phase of Hawaii's relationship with the U.S., transitioning it into a full-fledged state. Hawaii's strategic location in the Pacific Ocean and its unique cultural heritage contribute to its importance within the union.

The other options reflect states that joined the union earlier. Alaska became a state in 1959 as well but was second to Hawaii. Arizona joined in 1912, and New Mexico followed in the same year as well. Understanding Hawaii’s history and its admission to statehood helps to grasp the broader context of U.S. territorial expansion and state admissions.