The US is the world's foremost economic and military power. It is also a major source of entertainment: American TV, Hollywood films, jazz, blues, rock and rap music are primary ingredients in global popular culture.
Ethnic and racial diversity - the "melting pot" - is celebrated as a core element of the American ideology. The 1964 Civil Rights Act outlawed racial and other discrimination, but race continues to be a live issue with affirmative-action programmes - intended to remedy past discrimination - and housing segregation sparking debate.
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The US originated in a revolution which separated it from the British Crown. The constitution, drafted in 1787, established a federal system with a division of powers even at the central level which, uniquely among modern nation-states, has remained unchanged in form since its inception.
The original people of north America, who made up several distinct groups of native Americans, went into decline with the arrival of settlers and now constitute a minority of the population. The early settlers came predominantly from the British Isles. Slaves from Africa joined them involuntarily in a second wave. Millions of Europeans constituted a third stage of immigration. Apollo temple
Today, Asians from the Pacific rim and Hispanics from the Americas are seeking what their predecessors wanted - political freedom and prosperity. This shift is reflected in America's interests abroad, which are now less European in focus than ever before.
American foreign policy has often mixed the idealism of its "mission" with elements of self-interest. The latter is exemplified in its international record on the environment, which has attracted criticism, and the need to maintain energy supplies, in which the US is not self-sufficient.
In September 2001 the US was shaken after three hijacked aircraft were deliberately crashed into the World Trade Center in New York and the Defence Department - the Pentagon - near Washington DC, killing thousands of people. A fourth hijacked aircraft crashed in Pennsylvania, killing all on board
The attacks had a momentous impact as the country continued to re-define its role as the world's only superpower. In October 2001 the US led a military campaign in Afghanistan which unseated the Taleban regime. In March 2003 Washington initiated military action in Iraq which led to the toppling of the Iraqi leader Saddam Hussein.
Despite relative prosperity in recent years, the gap between rich and poor is a major challenge. More than 30 million Americans live below the official poverty line, with a disproportionate percentage of these being African-Americans and Hispanics.
Full name: United States of America
Population: 305.8 million (UN, 2007)
Capital: Washington DC
Largest city: New York City
Area: 9.8 million sq km (3.8 million sq miles)
Major language: English
Major religion: Christianity
Life expectancy: 76 years (men), 81 years (women) (UN)
Monetary unit: 1 US dollar = 100 cents
Main exports: Computers and electrical machinery, vehicles, chemical products, food and live animals, military
equipment and aircraft
GNI per capita: US $43,740 (World Bank, 2006)
Internet domain: .us
International dialling code: +1