How many states were admitted into the Union of the United States in the twentieth century?

Five states were added during the 20th century. They are Oklahoma (Nov. 16, 1907), New Mexico (Jan. 6, 1912), Arizona (Feb. 14, 1912), Alaska (Jan. 3, 1959), and Hawaii (Aug. 21, 1959).

The original 13 colonies were a group of British territories in North America. They were founded in the 17th and 18th centuries and became the thirteen colonies in 1776, when they declared independence. The colonies became states of the new nation in 1788, when New Hampshire became the ninth and final necessary state to ratify the United States Constitution.

The Constitution went into effect on June 21,1788, after ratification by 9 of the 13 states, and the federal government began operations under it on March 4, 1789. The Admission to the Union Clause of the United States Constitution, often called the New States Clause is found at Article IV, Section 3, Clause 1. It authorizes the Congress to admit new states into the United States beyond the thirteen already in existence at the time the Constitution went into effect.

Since then, 37 additional states have been admitted into the Union. Each new state has been admitted on an equal footing with those already in existence. The 50 stars on the U.S. flag represent the 50 states of the United States of America in 2019. In 1896 the U.S. flag had 45 stars with the admission of Utah. Since then five further stars have been added for Oklahoma , New Mexico, Arizona, Alaska, and Hawaii.