
The United States of America is a federal constitutional republic comprised of 50 states, one federal district, and several insular territories. Situated largely in the western hemisphere, its forty-eight contiguous states and the District of Columbia (coextensive with Washington, the capital) lie in central North America between the Pacific and Atlantic Oceans, bounded 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. Insular areas are scattered throughout the Americas and Pacific.
At over 3.7 million square miles (over 9.6 million kmІ) 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. A liberal democracy, the U.S. is one of the world's most ethnically and socially diverse nations .American society is the product of large-scale immigration and is home to a complex social structure as well as a wide array of household arrangements. Its national economy is the world's largest, with a 2006 Gross Domestic Product (GDP) of more than $13 trillion.



