The United States of America, usually referred to as the United States, the USA, 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. Proclaiming themselves "states," they issued the Declaration of Independence on July 4, 1776. 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. The Bill of Rights, comprising ten constitutional amendments, 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. However, the Jim Crow laws passed after reconstruction allowed racism and inequality to persist. 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.
The United States has a capitalist mixed economy, which is fueled by abundant natural resources, a well-developed infrastructure, and high productivity. According to the International Monetary Fund, the United States GDP of more than $13 trillion constitutes over 25.5% of the gross world product at market exchange rates and over 19% of the gross world product at purchasing power parity (PPP). The largest national GDP in the world, it was slightly less than the combined GDP of the European Union at PPP in 2006. The country ranks eighth in the world in nominal GDP per capita and fourth in GDP per capita at PPP. The United States is the largest importer of goods and third largest exporter, though exports per capita are relatively low. Canada, China, Mexico, Japan, and Germany are its top trading partners. The leading export commodity is electrical machinery, while vehicles constitute the leading import.
The private sector constitutes the bulk of the economy, with government activity accounting for 12.4% of GDP. The economy is postindustrial, with the service sector contributing 67.8% of GDP. The leading business field by gross business receipts is wholesale and retail trade; by net income it is finance and insurance. The United States remains an industrial power, with chemical products the leading manufacturing field. The United States is the third largest producer of oil in the world. It is the world's number one producer of electrical and nuclear energy, as well as liquid natural gas, sulfur, phosphates, and salt. While agriculture accounts for just under 1% of GDP,the United States is the world's top producer of corn and soybeans. The country's leading cash crop is marijuana, despite federal laws making its cultivation and sale illegal. The New York Stock Exchange is the world's largest by dollar volume. Coca-Cola and McDonald's are the two most recognized brands in the world. In 2005, 155 million persons were employed with earnings, of whom 80% worked in full-time jobs. The majority, 79%, were employed in the service sector. With approximately 15.5 million people, health care and social assistance is the leading field of employment. About 12% of American workers are unionized, compared to 30% in Western Europe. The U.S. ranks number one in the ease of hiring and firing workers, according to the World Bank. Between 1973 and 2003, a year's work for the average American grew by 199 hours. Partly as a result, the United States maintains the highest labor productivity in the world. However, it no longer leads the world in productivity per hour as it did from the 1950s through the early 1990s; workers in Norway, France, Belgium, and Luxembourg are now more productive per hour. The United States ranks third in the World Bank's Ease of Doing Business Index. Compared to Europe, U.S. property and corporate income taxes are generally higher, while labor and, particularly, consumption taxes are lower.
Science and technology
The United States has been a leader in scientific research and technological innovation since the late nineteenth century. In 1876, Alexander Graham Bell was awarded the first U.S. patent for the telephone. The laboratory of Thomas Edison developed the phonograph, the first long-lasting light bulb, and the first viable movie camera. In the early twentieth century, the automobile companies of Ransom E. Olds and Henry Ford pioneered assembly line manufacturing. The Wright brothers, in 1903, made what is recognized as the "first sustained and controlled heavier-than-air powered flight." The rise of Nazism in the 1930s led many important European scientists, including Albert Einstein and Enrico Fermi, to immigrate to the United States. During World War II, the U.S.-based Manhattan Project developed nuclear weapons, ushering in the Atomic Age. The Space Race produced rapid advances in rocketry, materials science, and computers. The United States largely developed the ARPANET and its successor, the Internet. Today, the bulk of research and development funding, 64%, comes from the private sector.The United States leads the world in scientific research papers and impact factor. Americans enjoy high levels of access to technological consumer goods, and almost half of U.S. households have broadband Internet service. The country is the primary developer and grower of genetically modified food; more than half of the world's land planted with biotech crops is in the United States.
Mainstream American culinary arts are similar to those in other Western countries. Wheat is the primary cereal grain. Traditional American cuisine uses ingredients such as turkey, white-tailed deer venison, potatoes, sweet potatoes, corn, squash, and maple syrup, indigenous foods employed by Native Americans and early European settlers. Slow-cooked pork and beef barbecue, crab cakes, potato chips, and chocolate chip cookies are distinctively American styles. Soul food, developed by African slaves, is popular around the South and among many African Americans elsewhere. Syncretic cuisines such as Louisiana creole, Cajun, and Tex-Mex are regionally important. Characteristic dishes such as apple pie, fried chicken, pizza, hamburgers, and hot dogs derive from the recipes of various immigrants. French fries, Mexican dishes such as burritos and tacos, and pasta dishes freely adapted from Italian sources are widely consumed. Americans generally prefer coffee to tea. Marketing by U.S. industries is largely responsible for making orange juice and milk ubiquitous breakfast beverages. During the 1980s and 1990s, Americans' caloric intake rose 24%; frequent dining at fast food outlets is associated with what health officials call the American "obesity epidemic." Highly sweetened soft drinks are widely popular; sugared beverages account for 9% of the average American's caloric intake.