The United States of America (USA), commonly known as the United States (U.S. or US), America or the States, is a country mostly located in central North America, between Canada and Mexico. It consists of 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles (9.8 million km2), it is the world's third- or fourth-largest country by total area. With a 2019 estimated population of over 328 million, the U.S. is the third most populous country in the world. The 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. Numerous disputes between Great Britain and the colonies led to the American Revolutionary War lasting between 1775 and 1783, leading to independence. Beginning in the late 18th century, the United States vigorously expanded across North America, gradually acquiring new territories, killing and displacing Native Americans, and admitting new states. By 1848, the United States spanned the continent.Slavery had been legal in much of the United States (and provided much of the labor force necessary for the country's economic power) from the 17th to second half of the 19th century, when the American Civil War led to its abolition.
