The
United States of America—usually referred to as
the United States, the U.S., or
America—is a constitutional federal 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, and 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 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 by
population. The United States is one of the world's most ethnically
diverse nations, the product of large-scale immigration from many
countries. The U.S. economy is the largest national economy in the
world, with a nominal 2006 gross domestic product (GDP) of more
than US$13 trillion (over 25% of the world total based on nominal
GDP and almost 20% by purchasing power parity).
The nation
was founded by thirteen colonies of Great Britain located along the
Atlantic seaboard. On July 4, 1776, they jointly issued the
Declaration of Independence, which proclaimed their independence
from Great Britain and their formation of a cooperative union. The
rebellious states defeated Great Britain in the American
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 with a
strong central government. The Bill of Rights, comprising ten
constitutional amendments guaranteeing many fundamental civil
rights and freedoms, was ratified in 1791.
In the
nineteenth century, the United States acquired land from France,
Spain, the United Kingdom, Mexico, and Russia, and annexed the
Republic of Texas and the Republic of Hawaii. Disputes between the
agrarian South and industrial North over states' rights and the
expansion of the institution of slavery provoked the American Civil
War of the 1860s. The North's victory prevented a permanent split
of the country and led to the end of legal slavery in the United
States. The Spanish-American War and World War I confirmed the
nation's status as a military power. In 1945, the United States
emerged from World War II as the first country with nuclear
weapons, a permanent member of the United Nations Security Council,
and a founding member of NATO. In the post–Cold War era, the United
States is the only remaining superpower—accounting for
approximately 50% of global military spending—and a dominant
economic, political, and cultural force in the world.