United States

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, nine Minor Outlying Islands,^[i] and 326 Indian reservations. The United States is the world's third-largest country by both land and total area.^[c] It shares land borders with Canada to its north and with Mexico to its south and has maritime borders with the Bahamas, Cuba, Russia, and other nations.^[j] With a population of over 333 million,^[k] it is the most populous country in the Americas and the third most populous in the world. The national capital of the United States is Washington, D.C., and its most populous city and principal financial center is New York City.

Indigenous peoples have inhabited the Americas for thousands of years. Beginning in 1607, British colonization led to the establishment of the Thirteen Colonies in what is now the Eastern United States. They quarreled with the British Crown over taxation and political representation, leading to the American Revolution and proceeding Revolutionary War. The United States declared independence on July 4, 1776, becoming the first nation-state founded on Enlightenment principles of unalienable natural rights, consent of the governed, and liberal democracy. During the nineteenth century, the United States political philosophy was influenced by the concept of manifest destiny, as the country expanded across the continent in a number of wars, land purchases, and treaties, eventually reaching the Pacific Ocean by the middle of the century. Sectional division surrounding slavery in the Southern United States led to the secession of the Confederate States of America, which fought the remaining states of the Union during the American Civil War (1861–1865). With the Union's victory and preservation, slavery was abolished nationally by the Thirteenth Amendment.

By 1900, the United States had established itself as a world power, becoming the world's largest economy. After Japan's attack on Pearl Harbor in 1941, the U.S. entered World War II on the Allied side. The aftermath of the war left the United States and the Soviet Union as the world's two superpowers and led to the Cold War. During the Cold War, both countries engaged in a struggle for ideological dominance but avoided direct military conflict. They also competed in the Space Race, which culminated in the 1969 landing of Apollo 11, making the U.S. the first and only nation to ever land humans on the Moon. With the Soviet Union's collapse and the subsequent end of the Cold War in 1991, the United States emerged as the world's sole superpower.

The United States government is a federal republic and a representative democracy with three separate branches of government. It has a bicameral national legislature composed of the House of Representatives, a lower house; and the Senate, an upper house based on equal representation for each state. Many policy issues are decentralized, with widely differing laws by jurisdiction. The U.S. ranks highly in international measures of quality of life, income and wealth, economic competitiveness, human rights, innovation, and education; it has low levels of perceived corruption and the highest median income per person of any polity in the world. It has high levels of incarceration and inequality and lacks universal health care. As a melting pot of cultures and ethnicities, the U.S. has been shaped by the world's largest immigrant population.