UNITED STATE OF AMERICA

The United States of America is a country of the western hemisphere, comprising fifty states and several territories. Forty-eight contiguous states 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. The United States is a federal constitutional republic with Washington, D.C. its capital.

At over 3.7 million square miles (over 9.6 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 population.[4] With a gross domestic product (GDP) of more than $13 trillion, the U.S. has the largest national economy in the world. GDP per capita ranks the U.S. first among large economies.

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.The U.S. is one of the world's most ethnically and socially diverse nations.

The nation was founded by thirteen colonies declaring their independence from Great Britain on July 4, 1776. It adopted the current constitution (which has been amended several times subsequently) on September 17, 1787. The country greatly expanded in territory throughout the 19th century, acquiring further territory from the United Kingdom, as well as lands from France, Mexico, Spain, and Russia. With the collapse of the Soviet Union in 1991, it became the world's sole remaining superpower, and is a declared nuclear weapons state. The United States continues to exert dominant economic, political, cultural and military influence around the globe.

The United States is the world's third or fourth largest country by total area, and the third largest by land area alone, after Russia and China and just ahead of Canada.[16] Its contiguous portion is bounded by the North Atlantic Ocean to the east, the North Pacific Ocean to the west, Mexico and the Gulf of Mexico to the south, and Canada to the north. Alaska (the largest state in area) is bound by Canada to its east, with the Pacific Ocean to its south, the Arctic Ocean to its north, and the Bering Strait to the west. The state of Hawaii occupies an archipelago in the Pacific Ocean, southwest of the North American mainland.

Deciduous vegetation and grasslands prevail in the eastern U.S., transitioning to prairies, boreal forests, and the Rocky Mountains in the west, and deserts in the southwest. In the northeast, the coasts of the Great Lakes and Atlantic seaboard host much of the country's population.

The U.S. has an extremely varied geography. The eastern seaboard has a coastal plain which is widest in the south and narrows in the north. The coastal plain does not exist north of New Jersey, although there are glacial outwash plains on Long Island, Martha's Vineyard, and Nantucket. In the extreme southeast, Florida is home to the ecologically unique Everglades.

Beyond the coastal plain, the rolling hills of the Piedmont region end at the Appalachian Mountains, which rise above 6,000 feet (1,830 m) in North Carolina, Tennessee, and New Hampshire. From the west slope of the Appalachians, the Interior Plains of the Midwest are relatively flat and are the location of the Great Lakes as well as the Mississippi-Missouri River, the world's 4th longest river system.[17] West of the Mississippi River, the Interior Plains slope uphill and blend into the vast and often featureless Great Plains.

The abrupt rise of the Rocky Mountains, at the western edge of the Great Plains, extends north to south across the continental U.S., reaching altitudes higher than 14,000 feet (4,270 m) in Colorado.[18] In the past, the Rocky Mountains had a higher level of volcanic activity; nowadays, the range only has one area of volcanism (the supervolcano underlying Yellowstone National Park in Wyoming, possibly the world's largest volcano), although rift volcanism has occurred relatively recently near the Rockies' southern margin in New Mexico.[19]

Alaska has numerous mountain ranges; including Mount McKinley (Denali), the highest peak in North America. Numerous volcanoes can be found throughout the Alexander and Aleutian Islands extending south and west of the Alaskan mainland.

The Hawaiian Islands are tropical, volcanic islands extending over 1,500 miles (2,400 km), and consisting of six larger islands and another dozen smaller ones that are inhabited.

Due to its large size and wide range of geographic features, the United States contains examples of nearly every global climate. The climate is temperate in most areas, tropical in Hawaii and southern Florida, polar in Alaska, semiarid in the Great Plains west of the 100th meridian, deserts in the Southwest, Mediterranean in coastal California and arid in the Great Basin. Its comparatively generous climate contributed (in part) to the country's rise as a world power, with infrequent severe drought in the major agricultural regions, a general lack of widespread flooding, and a mainly temperate climate that receives adequate precipitation.

The United States has a long-standing tradition of civilian control of military affairs. The Department of Defense administers the U.S. armed forces, which comprise the Army, the Navy, the Marine Corps, and the Air Force. The Coast Guard falls under the jurisdiction of the Department of Homeland Security in peacetime but is placed under the Department of the Navy in times of war. The military of the United States comprises 1.4 million personnel on active duty,[37] along with several hundred thousand each in the Reserves and the National Guard. Service in the military is voluntary, though conscription may occur in times of war through the Selective Service System. The United States is considered to have the most powerful military in the world, partly because of the size of its defense budget; American defense expenditures in 2005 were estimated to be greater than the next 14 largest national military budgets combined,[38] even though the U.S. military budget is only about 4% of the country's gross domestic product.[39][40] The U.S. military maintains more than 700 bases and facilities, distributed throughout every continent except Antarctica.[41] Much of U.S. military capability is involved in logistics and transportation, which enable rapid buildup of forces as needed. The Air Force maintains a large fleet of C-5 Galaxy, C-17 Globemaster, and C-130 Hercules transportation aircraft with an equally large fleet of aerial refueling tankers. The Marine Corps maintains Marine Expeditionary Units at sea with the Navy's Atlantic and Pacific Fleets. The Navy's fleet of 11 active aircraft carriers, combined with a military doctrine of power projection, enables a flexible response to potential threats. For these reasons, the United States military is universally considered the most powerful in the world.