States by date of admission to the Union were the last to join.

The United States Congress officially adopted the Declaration of Independence in the summer of 1776.Today's America is very different from the U.S.A. of 1776.Today, there are 50 states, many of which weren't granted statehood until the 20th century.Which states are the youngest?More about the last U.S. states to join the Union can be found here.These 30 Things in History Textbooks That Weren't There Just 10 Years ago are good for American history lessons.

Oklahoma's journey to statehood is complicated.When the land was split into Oklahoma Territory and Indian Territory, local and federal politicians argued over whether the territory should be made into a single state or two states.On June 16, 1906, Republican President Theodore Roosevelt signed the Oklahoma Enabling Act, which made Oklahoma a single state, because he feared that giving the Indigenous peoples their own state could lead to a Democratic majority.The Union was officially entered on November 16, 1907.

New Mexico was part of the former Spanish colony of Mexico until it became an independent country in 1848.After the Mexican-American war, the United States received a large amount of land in New Mexico.On January 6, 1912, the two pieces of land were officially made into one state after the U.S. government bought the rest of New Mexico from the Mexican government.

Arizona was the last mainland state to become a state.On February 14, 1912, the Grand Canyon State became a state after Phoenix became one of the fastest-growing cities in the country.When Arizona won the Mexican-American War in 1863, it became a U.S. territory.

On January 3, 1959 Alaska became the 49th state in the Union.The majority of Americans were unhappy with the U.S. government when they purchased the land from the Russians in 1867.

According to The New York Times, people referred to this 586,000- square-mile area as "Seward's icebox" until 1896, when gold was discovered in the Yukon Territory and suddenly people became interested in what the vast land had to offer.In order to prevent a mainland attack during World War II, several military bases were established in Alaska.

The 50th and final state was Hawaii.The group of islands were part of America before that.The Roy Rosenzweig Center for History and New Media at George Mason University states that Hawaii became a U.S. territory in 1898 and that 94.3% of residents voted for statehood after World War II.Don't miss these 17 crazy historical facts that are worth repeating over and over.