At over 3.7 million square miles (over 9.6 million km²) and with more than 300 million people, the United States is the third or fourth largest country by total area, and third largest by land area and population.[4] American society is the product of large-scale immigration and is home to a complex social structure[5] as well as a wide array of household arrangements.[6] The U.S. is one of the world's most ethnically and socially diverse nations.[7] The United States had the largest national economy with a GDP of over $13 trillion, constituting 22% of gross world product.[8] In terms of GDP per capita the US ranks 3rd and 8th, depending on measurement.[9]

The nation was founded by thirteen colonies of Great Britain who issued the Declaration of Independence on July 4, 1776. It adopted the current constitution on September 17, 1787 making 27 amendments afterwards. The country greatly expanded in territory throughout the 19th century, acquiring further territory from France, Mexico, Spain, and Russia. The United States became one of two major superpowers due to its role in World War II and its development of nuclear weapons. The remaining superpower after the collapse of the Soviet Union, the United States continues to exert dominant economic, political, cultural, and military influence around the globe.[10]