United States of America

UNITED STATES OF AMERICA

The 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 by population. The United States is one of the world's most ethnically diverse nations, the product of large-scale immigration from many countries.[6] Its national economy is the largest in the world, with a nominal 2006 gross domestic product (GDP) of more than US$13 trillion.[3]
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 American Revolutionary War, the first successful colonial war of independence.[7]
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. The Bill of Rights, comprising ten constitutional amendments, was ratified in 1791. In the nineteenth century, the United States acquired land from France, Spain, Mexico, and Russia, and annexed the Republic of Texas and the Republic of Hawaii. The American Civil War ended slavery in the United States and prevented a permanent split of the country. The Spanish-American War and World War I confirmed its status as a military power. In 1945, the United States emerged from World War II as the first country with nuclear weapons and a permanent member of the United Nations Security Council. The sole remaining superpower in the post–Cold War era, the United States is perceived by many as the dominant economic, political, cultural, and military force in the world.[8]

ETYMOLOGY
Common abbreviations of the United States of America include the United States, the U.S., and the U.S.A. Colloquial names for the country include the common America as well as the States. The term

Americas, for the lands of the western hemisphere, was coined in the early sixteenth century after Amerigo Vespucci, an Italian explorer and cartographer. The full name of the country was first used officially in the Declaration of Independence, which was the "unanimous Declaration of the thirteen united States of America" adopted by the "Representatives of the united States of America" on July 4, 1776.[9] The current name was finalized on November 15, 1777, when the Second Continental Congress adopted the Articles of Confederation, the first of which states, "The Stile of this Confederacy shall be 'The United States of America.'" Columbia, a once popular name for the Americas and the United States, was derived from Christopher Columbus. It appears in the name District of Columbia. A female personification of Columbia appears on some official documents, including certain prints of U.S. currency.
The standard way to refer to a citizen of the United States is as an American. Though United States is the formal adjective, American and U.S. are the most common adjectives used to refer to the country ("American values," "U.S. forces"). American is rarely used in English to refer to people not connected to the United States.

GEORGEPHY
Main articles:

Geography of the United States and Territorial evolution of the United States
Topographic map of the continental United States

The United States is the world's third or fourth largest nation by total area, before or after the People's Republic of China, depending on how two territories disputed by China and India are counted. Including only land area, the United States is third in size behind Russia and China, just ahead of Canada.[10] The continental United States stretches from the Atlantic Ocean to the Pacific Ocean and from Canada to Mexico and the Gulf of Mexico. Alaska is the largest state in area. Separated by Canada, it touches the Pacific and Arctic Oceans. Hawaii occupies an archipelago in the Pacific, southwest of North America. The commonwealth of Puerto Rico, the largest and most populous U.S. territory, is in the northeastern Caribbean. With a few exceptions, such as the territory of Guam and the westernmost portions of Alaska, nearly all of the country lies in the western hemisphere.


Climate zones of the continental United States
The coastal plain of the Atlantic seaboard gives way further inland to deciduous forests and the rolling hills of the Piedmont. The Appalachian Mountains divide the eastern seaboard from the Great Lakes and the grasslands of the Midwest. The Mississippi-Missouri River, the world's fourth longest river system, runs mainly north-south through the heart of the country. The flat, fertile prairie land of the Great Plains stretches to the west. The Rocky Mountains, at the western edge of the Great Plains, extend north to south across the continental United States, reaching altitudes higher than 14,000 feet (4,300 m) in Colorado.[11] The area to the west of the Rockies is dominated by deserts such as the Mojave and the rocky Great Basin. The Sierra Nevada range runs parallel to the Rockies, relatively close to the Pacific coast. At 20,320 ft (6,194 m), Alaska's Mount McKinley is the country's tallest peak. Active volcanoes are common throughout the Alexander and Aleutian Islands and the entire state of Hawaii is built upon tropical volcanic islands. The supervolcano underlying Yellowstone National Park in the Rockies is the continent's largest volcanic feature.[12]
Because of the United States' large size and wide range of geographic features, nearly every type of climate is represented. 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, desert in the Southwest, Mediterranean in coastal California

, and arid in the Great Basin. Extreme weather is not uncommon—the states bordering the Gulf of Mexico are prone to hurricanes and most of the world's tornadoes occur within the continental United States, primarily in the Midwest.