United States of America

The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territories, 326 Indian reservations, and nine minor outlying islands. At nearly 3.8 million square miles (9.8 million square kilometers), it is the world's fourth-largest country by land area and third-largest by total area. The United States shares land and maritime borders with Canada to the north and Mexico to the south as well as maritime borders with the Bahamas, Cuba, and Russia. With more than 331 million people, it is the third most populous country in the world. The national capital is Washington, D.C., and the most populous city and financial center is New York City.
Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago, and European colonization began in the 16th century. The United States emerged from the Thirteen British Colonies established along the East Coast. Disputes with Great Britain over taxation and political representation led to the American Revolutionary War (1775–1783), which established the nation's independence. In the late 18th century, the U.S. began expanding territory across North America, gradually obtaining new territories, sometimes through war, frequently displacing Native Americans, and admitting new states. The enslavement of African Americans was legal in the southern United States until the second half of the 19th century, when the American Civil War led to its abolition. The Spanish–American War and World War I established the U.S. as a world power, and the aftermath of World War II left the United States and the Soviet Union as the world's two superpowers. During the Cold War, both countries fought in the Korean and Vietnam War but avoided direct armed conflict. The two nations competed in the Space Race, culminating in the 1969 American spaceflight that first landed humans on the Moon. The Soviet Union's dissolution in 1991 ended the Cold War, leaving the United States as the world's sole superpower. In the post–Cold War era, the United States has engaged in several conflicts in the Middle East.
The United States is a federal presidential constitutional republic with three separate branches of government, including a bicameral legislature. It is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States, and other international organizations. It is a permanent member of the United Nations Security Council. The United States is a member of multiple military alliances, including NATO, AUKUS, and unilateral alliances with Japan, South Korea, and the Philippines. Considered a melting pot of cultures and ethnicities, its population has been profoundly shaped by centuries of immigration. The United States is a liberal democracy; it ranks high in international measures of economic freedom, quality of life, education, and human rights; and it has low levels of perceived corruption. Unlike other western democracies, the United States lacks universal health care, retains capital punishment, and has high levels of incarceration and inequality.The United States is a highly developed country, and its economy accounts for approximately a quarter of global GDP and is the world's largest by GDP at market exchange rates. By value, the United States is the world's largest importer and second-largest exporter of goods. Although its population is only 4.2% of the world's total, it holds over 30% of the total wealth in the world, the largest share held by any country. Making up more than a third of global military spending, the United States is the foremost military power in the world and a leading political, cultural, and scientific force.