The United States of America (commonly referred to as the United States, the U.S., the USA, the States, or America) is a federal constitutional republic comprising fifty states and a federal district. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D.C., the capital district, lie 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 Russia to the west across the Bering Strait. The state of Hawaii is an archipelago in the mid-Pacific. The country also possesses several territories, or insular areas, scattered around the Caribbean and Pacific.
At 3.79 million square miles (9.83 million km²) and with about 305 million people, the United States is the third or fourth largest country by total area, and third largest by land area and by population. The United States is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries. The U.S. economy is the largest national economy in the world, with an estimated 2008 gross domestic product (GDP) of US$14.3 trillion (23% of the world total based on nominal GDP and almost 21% at purchasing power parity).
The United States is a multicultural nation, home to a wide variety of ethnic groups, traditions, and values. There is no "American" ethnicity; aside from the now small Native American and Native Hawaiian
populations, nearly all Americans or their ancestors immigrated within the past five centuries. The culture held in common by most Americans is referred to as mainstream American culture, a Western culture
largely derived from the traditions of Western European migrants, beginning with the early English and Dutch settlers.
German, Irish, and Scottish cultures have also been very influential. Certain cultural attributes of Mandé and Wolof slaves from West Africa were adopted by the American mainstream; based more on the
traditions of Central African Bantu slaves, a distinct African American culture developed that would also deeply affect the mainstream. Westward expansion integrated the Creoles and Cajuns of Louisiana
and the Hispanos of the Southwest and brought close contact with the culture of Mexico. Large-scale immigration in the late nineteenth and early twentieth centuries from Southern and Eastern Europe
introduced many new cultural elements. More recent immigration from Asia and especially Latin America has had broad impact. The resulting cultural mix may be described as a homogeneous melting pot,
or as a pluralistic salad bowl in which immigrants and their descendants retain distinctive cultural characteristics.