United States

The United States of America (USA), also known as the United States (U .) or America, is a country primarily located in North America. It is a federal republic consisting of 50 states and a federal capital district, Washington, D . The 48 contiguous states border Canada to the north and Mexico to the south, with the semi-exclave of Alaska in the northwest and the archipelago of Hawaii in the Pacific Ocean. The United States also asserts sovereignty over five major island territories and various uninhabited islands in Oceania and the Caribbean. It is a megadiverse country, with the world's third-largest land area and third-largest population, exceeding 341 million. Paleo-Indians first migrated from North Asia to North America at least 15,000 years ago, and formed various civilizations. European discovery of the Americas began in 1492, and British colonization followed with the 1607 settlement of Virginia, the first of the Thirteen Colonies. The American Enlightenment that spread throughout the colonies in the 18th century valued republicanism and liberalism. Clashes with the British Crown over taxation without parliamentary representation and the denial of other English rights evolved into the American Revolution, which led to the Declaration of Independence on July 4, 1776. Victory in the 1775–1783 Revolutionary War brought international recognition of the country's sovereignty. Rapid westward territorial expansion followed the purchase, settlement, and conquest of European-held or Indigenous-controlled territory. As more states were admitted into the Union, a North–South division over slavery led 11 Southern states to declare secession and join as the Confederate States of America in order to preserve slavery there. These states fought against the Union in the American Civil War of 1861–1865 but were defeated. With the United States' victory and reunification, slavery was abolished nationally. By 1900, the country had established itself as a great power, a status solidified after its involvement during World War I. Following Japan's attack on Pearl Harbor in 1941, the U . entered World War II on the side of the Allies. Its aftermath left the U . and the Soviet Union as rival superpowers, competing for ideological dominance and international influence during the Cold War. The Soviet Union's collapse in 1991 left the U . the world's sole superpower. The U . federal government is a representative democracy with a president and a constitution that creates a separation of powers among three branches: legislative, executive, and judicial. The United States Congress is a bicameral national legislature composed of the House of Representatives (a lower house based on population) and the Senate (an upper house based on equal representation for each state). Federalism grants substantial autonomy to the 50 states. In addition, 574 Native American tribes have sovereignty rights, and there are 326 Native American reservations. A developed country, the U . ranks high in economic competitiveness, innovation, and higher education. Accounting for over a quarter of nominal global GDP, the U . economy has been the world's largest since about 1890. It is the wealthiest country, with the highest disposable household income per capita among OECD members, though its wealth inequality is highly pronounced. Shaped by centuries of immigration, the culture of the U . is diverse and globally influential. Making up a third of global military spending, the country is widely considered to have the most powerful armed forces in the world and was the first to develop and employ nuclear weapons. A member of numerous international organizations including the United Nations Security Council, it plays a major role in global political, cultural, economic, and military affairs.