The United States of America (USA), commonly known as the United States (US or U.S.) or America, is a country primarily located in central North America, between Canada and Mexico. It consists of 50 states, a federal district, five self-governing territories, and several other island possessions.^[h] At 3.8 million square miles (9.8 million square kilometers), it is the world's third- or fourth-largest country by total area.^[d] With a population of over 328 million, it is the third most populous country in the world. The national capital is Washington, D.C., and the most populous city 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 over taxation and political representation with Great Britain led to the American Revolutionary War (1775–1783), which established independence. In the late 18th century, the U.S. began vigorously expanding across North America, gradually acquiring new territories, conquering and displacing Native Americans, and admitting new states; by 1848, the United States spanned the continent. Slavery 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, a status confirmed by the outcome of World War II. During the Cold War, the United States and the Soviet Union engaged in various proxy wars, but avoided direct military conflict. They also competed in the Space Race, culminating in the 1969 spaceflight that first landed humans on the Moon. The Soviet Union's collapse in 1991 ended the Cold War and left the United States as the world's sole superpower.