The United States of America (U.S.A. or USA), commonly known as the Un

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 some minor possessions.[g] At 3.8 million square miles (9.8 million square kilometers), it is the world's third- or fourth-largest country by total area.[c] With a population of 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 is New York City.has been generally accepted that the first inhabitants of North America migrated from Siberia by way of the Bering land bridge and arrived at least 12,000 years ago; however, some evidence suggests an even earlier date of arrival.[32][33][34] The Clovis culture, which appeared around 11,000 BC, is believed to represent the first wave of human settlement of the Americas.[35][36] This was likely the first of three major waves of migration into North America; later waves brought the ancestors of present-day Athabaskans, Aleuts, and Eskimos.[37]

Over time, indigenous cultures in North America grew increasingly complex, and some, such as the pre-Columbian Mississippian culture in the southeast, developed advanced agriculture, architecture, and complex societies.[38] The city-state of Cahokia is the largest, most complex pre-Columbian archaeological site in the modern-day United States.[39] In the Four Corners region, Ancestral Puebloan culture developed from centuries of agricultural experimentation.[40] The Haudenosaunee, located in the southern Great Lakes region, was established at some point between the twelfth and fifteenth centuries.[41] Most prominent along the Atlantic coast were the Algonquian tribes, who practiced hunting and trapping, along with limited cultivation.

Estimating the native population of North America at the time of European contact is difficult.[42][43] Douglas H. Ubelaker of the Smithsonian Institution estimated that there was a population of 92,916 in the south Atlantic states and a population of 473,616 in the Gulf states,[44] but most academics regard this figure as too low.[42] Anthropologist Henry F. Dobyns believed the populations were much higher, suggesting around 1.1 million along the shores of the Gulf of Mexico, 2.2 million people living between Florida and Massachusetts, 5.2 million in the Mississippi Valley and tributaries, and around 700,000 people in the Florida peninsula