The United States of America, commonly known as the United States, or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major self-governing territories, 326 Indian reservations, and some minor possessions. At 3.8 million square miles, it is the world's third- or fourth-largest country by total area. With a population of more than 328 million people, 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, which established independence. In the late 18th century, the U.S. began vigorously expanding across North America, gradually acquiring new territories, frequently displacing Native Americans, and admitting new states; by 1848, the United States spanned the continent.