The United States of America (USA), commonly referred to as the United States (US), America, or simply the States, is a federal republic consisting of 50 states and a federal district. The 48 contiguous states and the federal district of Washington, D.C., are in central North America between Canada and Mexico. The state of Alaska is the northwestern part of North America and the state of Hawaii is an archipelago in the mid-Pacific. The country also has five populated and nine unpopulated territories in the Pacific and the Caribbean. At 3.79 million square miles (9.83 million km2) in total and with around 317 million people, the United States is the fourth-largest country by total area and third largest by population. It is one of the world’s most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries. The geography and climate of the United States is also extremely diverse, and it is home to a wide variety of wildlife.
Paleo-indians migrated from Asia to what is now the U.S. mainland around 15,000 years ago, with European colonization beginning in the 16th century. The United States emerged from 13 British colonies located along the Atlantic seaboard. Disputes between Great Britain and these colonies led to the American Revolution. On July 4, 1776, delegates from the 13 colonies unanimously issued the Declaration of Independence. The ensuing war ended in 1783 with the recognition of independence of the United States from the Kingdom of Great Britain, and was the first successful war of independence against a European colonial empire. The current Constitution was adopted on September 17, 1787. The first 10 amendments, collectively named the Bill of Rights, were ratified in 1791 and guarantee many fundamental civil rights and freedoms.
Driven by the doctrine of manifest destiny, the United States embarked on a vigorous expansion across North America throughout the 19th century. This involved displacing native tribes, acquiring new territories, and gradually admitting new states. The American Civil War ended legal slavery in the country. By the end of the 19th century, the United States extended into the Pacific Ocean, and its economy was the world’s largest. The Spanish–American War and World War I confirmed the country’s status as a global military power. The United States emerged from World War II as a global superpower, the first country with nuclear weapons, and a permanent member of the United Nations Security Council. The end of the Cold War and the dissolution of the Soviet Union left the United States as the sole superpower.
The United States is a developed country and has the world’s largest national economy, with an estimated GDP in 2013 of $16.7 trillion – 23% of global nominal GDP and 19% at purchasing-power parity. The economy is fueled by an abundance of natural resources and the world’s highest worker productivity, with per capita GDP being the world’s sixth-highest in 2010. While the U.S. economy is considered post-industrial, it continues to be one of the world’s largest manufacturers. The U.S. has the highest mean and second-highest median household income in the OECD as well as the highest average wage, though it has the fourth most unequal income distribution among OECD nations with roughly 16% of the population living in poverty. The country accounts for 39% of global military spending, being the world’s foremost economic and military power, a prominent political and cultural force, and a leader in scientific research and technological innovation.
The United States is home to many cultures and a wide variety of ethnic groups, traditions, and values. Aside from the relatively small Native American and Native Hawaiian populations, nearly all Americans or their ancestors settled or immigrated within the past five centuries. Mainstream American culture is a Western culture largely derived from the traditions of European immigrants with influences from many other sources, such as traditions brought by slaves from Africa. More recent immigration from Asia and especially Latin America has added to a cultural mix that has been described as both a homogenizing melting pot, and a heterogeneous salad bowl in which immigrants and their descendants retain distinctive cultural characteristics.
Core American culture was established by Protestant British colonists and shaped by the frontier settlement process, with the traits derived passed down to descendants and transmitted to immigrants through assimilation. Americans have traditionally been characterized by a strong work ethic, competitiveness, and individualism, as well as a unifying belief in an “American Creed” emphasizing liberty, equality, private property, democracy, rule of law, and a preference for limited government. Americans are extremely charitable by global standards. According to a 2006 British study, Americans gave 1.67% of GDP to charity, more than any other nation studied, more than twice the second place British figure of 0.73%, and around twelve times the French figure of 0.14%.
American culture is considered the most individualistic in the world. The American Dream, or the perception that Americans enjoy high social mobility, plays a key role in attracting immigrants. Whether this perception is realistic has been a topic of debate. While the mainstream culture holds that the United States is a classless society, scholars identify significant differences between the country’s social classes, affecting socialization, language, and values. Americans’ self-images, social viewpoints, and cultural expectations are associated with their occupations to an unusually close degree. While Americans tend greatly to value socioeconomic achievement, being ordinary or average is generally seen as a positive attribute.