he United States of America is a federal constitutional republic comprising fifty states and a federal district. The country is situated almost entirely in the western hemisphere: its forty-eight contiguous states and Washington, D.C., the capital district, lie in central North America between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the south; the state of Alaska is in the northwest of the continent with Canada to its east, and the state of Hawaii is in the mid-Pacific. The United States also possesses fourteen territories, or insular areas, that are scattered around the Caribbean and Pacific.

 

At 3.79 million square miles (9.83 million km²) and with over 300 million people, the United States is the third or fourth largest country by total area, and third largest by land area and population. The United States is one of the world's most ethnically diverse nations, the product of large-scale immigration from many countries. Its national economy is the largest in the world, with a nominal 2006 gross domestic product (GDP) of more than US$13 trillion.

 

The nation was founded by thirteen colonies of Great Britain located along the Atlantic seaboard. Proclaiming themselves "states," they issued the Declaration of Independence on July 4, 1776. The rebellious states defeated Britain in the Revolutionary War, the first successful colonial war of independence. A federal convention adopted the current United States Constitution on September 17, 1787; its ratification the following year made the states part of a single republic.