The **United States of America** (**USA**), commonly known as the **United States** (**U.S.** or **US**) or **America**, is a country [mostly located](https://en.wikipedia.org/wiki/Contiguous_United_States "Contiguous United States") in central [North America](https://en.wikipedia.org/wiki/North_America "North America"), between [Canada](https://en.wikipedia.org/wiki/Canada "Canada") and [Mexico](https://en.wikipedia.org/wiki/Mexico "Mexico"). It consists of 50 [states](https://en.wikipedia.org/wiki/U.S._state "U.S. state"), a [federal district](https://en.wikipedia.org/wiki/Washington,_D.C. "Washington, D.C."), 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 Americans are a racially and ethnically diverse population that has been shaped through centuries of immigration. The capital is [Washington, D.C.](https://en.wikipedia.org/wiki/Washington,_D.C. "Washington, D.C."), and the most populous cit is [New York City](https://en.wikipedia.org/wiki/New_York_City "New York City").