The United States of America (often shortened to the United States, USA, U.S.
or colloquially America) is a country of the western hemisphere comprising fifty states and numerous territories. Forty-eight contiguous states lie in central North America between the Pacific and Atlantic Oceans, bound on land by Canada to the north and Mexico to the south; Alaska is in the northwest of the continent with Canada to its east, and Hawaii is in the mid-Pacific. The United States is a federal constitutional republic; Washington, its capital, is coextensive with the District of Columbia (D.C.), the federal capital district
At over 3.7 million square miles (over 9.6 million km²) and with over 300 million people, the United States is the third largest country by both total area and population.  With a gros domestic product(GDP) of over $13 trillion, the U.S.
has the largest national economy in the world. GDP per capita ranks first among the larger economies of the world, and third eighth overall, depending on the measurement. The product of large-scale historical immigration and home to a complex social structure as well as a wide array of household arrangements, the U.S. is one of the world's most ethnically and socially diverse nations.