The present-day continental United States has been inhabited for at least 15,000 years by indigenous tribes. After European exploration and settlement in the 16th century, the English established their own colonies, and gained control of others begun by other European nations, in the eastern portion of the continent in the 17th and early 18th centuries. On 4 July 1776, at war with Britain over fair governance, thirteen of these colonies declared their independence; in 1783, the war ended in British acceptance of the new nation. Since then, the country has more than quadrupled in size: it now consists of 50 states and one federal district, and has a number of overseas territories.

At over 3.7 million square miles (over 9.5 million km²), the U.S. is the third or fourth largest country by area, depending on whether or not the disputed areas of China are included. It is also the world's third most populous nation, with nearly 300 million people.

The United States has maintained a liberal democratic political system since it adopted its Articles of Confederation on 1 March 1781 and the Constitution, the Articles' replacement, on 17 September 1787. American military, economic, cultural, and political influence increased throughout the 20th century; with the collapse of the Soviet Union at the end of the Cold War, the nation emerged as the world's sole remaining superpower. Today, the U.S. continues to play a leading role in world affairs.

History

Before the European colonization of the Americas, a process that began at the end of the 15th century, the present-day continental U.S. was inhabited exclusively by various indigenous tribes, including Alaskan Natives, who arrived on the continent over a period that may have begun 35,000 years ago and may have ended as recently as 11,000 years ago. The first confirmed European landing in the present-day United States was by a Spaniard, Juan Ponce de Leon, who landed in 1513 in Florida, and as part of his claim, the first European settlement was established by Don Pedro Menendez de Aviles on the site of a Timucuan Indian village in 1565 at St. Augustine, Florida.

The first successful English settlement was at Jamestown, Virginia, in 1607, followed in 1620 by the Pilgrims' landing at Plymouth, Massachusetts. In 1609 and 1617, respectively, the Dutch settled in part of what became New York and New Jersey. In 1638, the Swedes founded New Sweden, in part of what became Delaware, New Jersey, and Pennsylvania after passing through Dutch hands. Throughout the 17th and early 18th centuries, England (and later Great Britain) established new colonies, took over Dutch colonies, and split others. With the division of the Carolinas, in 1729, and the colonization of Georgia, in 1732, the British colonies in North America, excluding present-day Canada, numbered thirteen. These thirteen colonies would be drawn closer together over the coming decades.

Economy

The economic history of the United States is a story of economic growth that began with marginally successful colonial economies and progressed to the largest industrial economy in the world in the 20th and early 21st century.

The economic system of the United States can be described as a capitalist mixed economy, in which corporations, other private firms, and individuals make most microeconomic decisions, and governments prefer to take a smaller role in the domestic economy, although the combined role of all levels of government is relatively large, at 36% of the GDP. The U.S. has a small social safety net, and regulation of businesses is slightly below the average of developed countries. The United States' median household income in 2005 was $43,318.

Economic activity varies greatly across the country. For example, New York City is the center of the American financial, publishing, broadcasting, and advertising industries, while Los Angeles is the most important center for film and television production. The San Francisco Bay Area and the Pacific Northwest are major centers for technology. The Midwest is known for its reliance on manufacturing and heavy industry, with Detroit serving as the historic center of the American automotive industry, and Chicago serving as the business and financial capital of the region. The Southeast is a major area for agriculture, tourism, and the lumber industry, and, because of wages and costs below the national average, it continues to attract manufacturing.

The largest sector in the United States economy is services, which employs roughly three quarters of the work force.[45] The economy is fueled by an abundance in natural resources such as coal, petroleum, and precious metals. However, the country still depends for much of its energy on foreign countries. In agriculture, the country is a top producer of corn, soy beans, rice, and wheat, with the Great Plains labeled as the "breadbasket of the world" for their tremendous agricultural output. The U.S. has a large tourist industry, ranking third in the world, and is also a major exporter in goods such as airplanes, steel, weapons, and electronics. Canada accounts for 19% (more than any other nation) of the United States' foreign trade, followed by China, Mexico, and Japan.

While the per capita income of the United States is among the highest in the world, the wealth is comparatively concentrated, with approximately 40% of the population earning less than an average resident of western Europe and the top 20% earning substantially more. Since 1975, it has had what can be called a "two-tier" labor market, in which virtually all the real income gains have gone to the top 20% of households. This polarization is the result of a relatively high level of economic freedom.

The social mobility of U.S. residents relative to that of other countries is the subject of much debate. Some analysts have found that social mobility in the United States is low relative to other OECD states, specifically compared to Western Europe, Scandinavia and Canada. Low social mobility may stem in part from the U.S. educational system. Public education in the United States is funded mainly by local property taxes supplemented by state revenues. This frequently results in a wide difference in funding between poor districts or poor states and more affluent jurisdictions.  In addition, the practice of legacy preference at elite universities gives preference to the children of alumni, who are often wealthy. This practice reduces available spaces for better-qualified lower income students. Some analysts argue that relative social mobility in the U.S. peaked in the 1960s and declined rapidly beginning in the 1980s. Former Federal Reserve Board Chairman Alan Greenspan has also suggested that that the growing income inequality and low class mobility of the U.S. economy may eventually threaten the entire system in the near future.

The United States is an influential country in scientific and technological research and the production of innovative technological products. During World War II, the U.S. was the first to develop the atomic bomb, ushering in the atomic age. Beginning early the Cold War, the U.S. achieved successes in space science and technology, leading to a space race, which led to rapid advances in rocketry, weaponry, material science, computers, and many other areas. This technological progress was epitomized by the first visit of a man to the moon, when Neil Armstrong stepped off of Apollo 11 in July 1969.[59] The U.S. was also perhaps the most instrumental nation in the development of the Internet, through the funding of its predecessor, Arpanet, and the actual physical presence of much of the Internet.

In the sciences, Americans have a large share of Nobel Prizes, especially in the fields of physiology and medicine. The National Institutes of Health, a focal point for biomedical research in the United States, has contributed to the completion of the Human Genome Project.[60] The main governmental organization for aviation and space research is the National Aeronautics and Space Administration. Major corporations, such as Boeing and Lockheed Martin, also play an important role.

The automobile industry developed earlier and more rapidly in the United States than in most other countries. The backbone of the nation's transportation infrastructure is a network of high-capacity highways. From data taken in 2004, there are about 3,981,521 miles (6,407,637 km) of roadways in the U.S., the most in the world.[61]

Mass transit systems exist in large cities, such as New York, which operates one of the busiest subway systems in the world. With a few exceptions, American cities are less dense than those in other parts of the world. Low density partly results from and largely necessitates automobile ownership by most households.

Whereas the freight rail network is among the world's best (and most congested), the passenger rail network is underdeveloped by European and Japanese standards. This is partly due to the longer distances travelled in the U.S.; a destination two thousand miles away is reached more quickly by air than by rail. Government subsidies of air travel played a role in the bankruptcy of passenger-rail corporations in the 1970s. The U.S. had been unique in its high number of private passenger railroads. During the 1970s, government intervention reorganized freight railroads, and consolidated passenger service under the government-backed corporation Amtrak. No other country has more miles of rail than the U.S.

Air travel is the preferred means of travel for long distances. In terms of passengers, seventeen of the world's thirty busiest airports in 2004 were in the U.S., including the world's busiest, Hartsfield–Jackson Atlanta International Airport (ATL). In terms of cargo, in the same year, twelve of the world's thirty busiest airports were in the U.S., including the world's busiest, Memphis International Airport.

Several major seaports are in the United States; the three busiest are California's Port of Los Angeles and Port of Long Beach, and the Port of New York and New Jersey, all among the world's busiest. The Great Lakes also carry shipping traffic, the lakes being extensively connected to one another, the Mississippi River system, and the Atlantic Ocean. The first water link between the Great Lakes and the Atlantic, the Erie Canal, allowed the rapid expansion of agriculture and industry in the Midwest, and made New York City the economic center of the U.S.

Demographics

As of August 2006, there are an estimated 299,059,138 people in the United States, with a population growth rate of about 0.59%. The United States Census Bureau predicts that the population will surpass 300 million in October 2006. According to the 2000 census, about 79% of the population lives in urban areas, and the country has 31 ethnic groups with at least one million members each, with numerous others represented in smaller amounts.In terms of wealth distribution, thirty-five million Americans live in poverty, about 12.6% of the population; twenty percent of the population possesses 80% of the nation's wealth.

The majority of Americans (80.4% in 2004) are the descendants of white immigrants; people of solely non-Hispanic white ancestry were 67.4% of the population. The non-Hispanic white population is proportionally declining, both due to immigration from nonwhite countries and due to a higher birth rate among ethnic and racial minorities. If current immigration trends continue, the number of non-Hispanic whites is expected to be reduced to a plurality by 2040-2050. The largest ethnic group of European ancestry is German at 15.2%, followed by Irish (10.8%), English (8.7%), Italian (5.6%) and Scandinavian (3.7%). Many immigrants also hail from Slavic countries, such as Poland and Russia, as well as from French Canada. African Americans, or Blacks, largely descend from Africans who arrived as slaves during the seventeenth through nineteenth centuries, and number about 35 million or 12.9% of the population. At about 1.5% of the total population, Native Americans and Alaska Natives number about 4.4 million, approximately 35% of whom were living on reservations in 2005.

Current demographic trends include the immigration of Hispanics from Latin America into the Southwest, a region that is home to about 60% of the 35 million Hispanics in the United States. Immigrants from Mexico make up about 66% of the Hispanic community, and are second only to the German-descent population in the single-ethnicity category. The Hispanic population, which has been growing at an annual rate of about 4.46% since the 1990s, is expected to increase significantly in the coming decades, because of both immigration and a higher birth rate among Latinos than among the general population. According to the U.S. Bureau of the Census, the population of the United States will reach 300 million people in October 2006.